cypher_clause.c

/*
 * For PostgreSQL Database Management System:
 * (formerly known as Postgres, then as Postgres95)
 *
 * Portions Copyright (c) 1996-2010, The PostgreSQL Global Development Group
 *
 * Portions Copyright (c) 1994, The Regents of the University of California
 *
 * Permission to use, copy, modify, and distribute this software and its documentation for any purpose,
 * without fee, and without a written agreement is hereby granted, provided that the above copyright notice
 * and this paragraph and the following two paragraphs appear in all copies.
 *
 * IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST PROFITS,
 * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY
 * OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA
 * HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */

#include "postgres.h"

#include "access/heapam.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/optimizer.h"
#include "parser/parse_clause.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
#include "parser/parse_expr.h"
#include "parser/parse_func.h"
#include "parser/parse_oper.h"
#include "parser/parse_target.h"
#include "parser/parsetree.h"
#include "parser/parse_relation.h"
#include "rewrite/rewriteHandler.h"

#include "catalog/ag_graph.h"
#include "catalog/ag_label.h"
#include "commands/label_commands.h"
#include "parser/cypher_analyze.h"
#include "parser/cypher_clause.h"
#include "parser/cypher_expr.h"
#include "parser/cypher_item.h"
#include "parser/cypher_parse_agg.h"
#include "parser/cypher_transform_entity.h"
#include "utils/ag_cache.h"
#include "utils/ag_func.h"
#include "utils/ag_guc.h"

/*
 * Variable string names for makeTargetEntry. As they are going to be variable
 * names that will be hidden from the user, we need to do our best to make sure
 * they won't be picked by mistake. Additionally, their form needs to be easily
 * determined as ours. For now, prefix them as follows -
 *
 *     #define AGE_VARNAME_SOMETHING AGE_DEFAULT_VARNAME_PREFIX"something"
 *
 * We should probably make an automated variable generator, like for aliases,
 * for this.
 *
 * Also, keep these here as nothing outside of this file needs to know these.
 */
#define AGE_VARNAME_CREATE_CLAUSE AGE_DEFAULT_VARNAME_PREFIX"create_clause"
#define AGE_VARNAME_CREATE_NULL_VALUE AGE_DEFAULT_VARNAME_PREFIX"create_null_value"
#define AGE_VARNAME_DELETE_CLAUSE AGE_DEFAULT_VARNAME_PREFIX"delete_clause"
#define AGE_VARNAME_MERGE_CLAUSE AGE_DEFAULT_VARNAME_PREFIX"merge_clause"
#define AGE_VARNAME_ID AGE_DEFAULT_VARNAME_PREFIX"id"
#define AGE_VARNAME_SET_CLAUSE AGE_DEFAULT_VARNAME_PREFIX"set_clause"
#define AGE_VARNAME_SET_VALUE AGE_DEFAULT_VARNAME_PREFIX"set_value"

/*
 * In the transformation stage, we need to track
 * where a variable came from. When moving between
 * clauses, Postgres parsestate and Query data structures
 * are insufficient for some of the information we
 * need.
 */

/*
 * Rules to determine if a node must be included:
 *
 *      1. the node is in a path variable
 *      2. the node is a variable
 *      3. the node contains filter properties
 */
#define INCLUDE_NODE_IN_JOIN_TREE(path, node) \
    (path->var_name || node->name || node->props)

typedef Query *(*transform_method)(cypher_parsestate *cpstate,
                                   cypher_clause *clause);

/* projection */
static Query *transform_cypher_return(cypher_parsestate *cpstate,
                                      cypher_clause *clause);
static List *transform_cypher_order_by(cypher_parsestate *cpstate,
                                       List *sort_items, List **target_list,
                                       ParseExprKind expr_kind);
static TargetEntry *find_target_list_entry(cypher_parsestate *cpstate,
                                           Node *node, List **target_list,
                                           ParseExprKind expr_kind);
static Node *transform_cypher_limit(cypher_parsestate *cpstate, Node *node,
                                    ParseExprKind expr_kind,
                                    const char *construct_name);
static Query *transform_cypher_with(cypher_parsestate *cpstate,
                                    cypher_clause *clause);
static Query *transform_cypher_clause_with_where(cypher_parsestate *cpstate,
                                                 transform_method transform,
                                                 cypher_clause *clause,
                                                 Node *where);
/* match clause */
static Query *transform_cypher_match(cypher_parsestate *cpstate,
                                     cypher_clause *clause);
static Query *transform_cypher_match_pattern(cypher_parsestate *cpstate,
                                             cypher_clause *clause);
static List *transform_match_entities(cypher_parsestate *cpstate, Query *query,
                                      cypher_path *path);
static void transform_match_pattern(cypher_parsestate *cpstate, Query *query,
                                    List *pattern, Node *where);
static List *transform_match_path(cypher_parsestate *cpstate, Query *query,
                                  cypher_path *path);
static Expr *transform_cypher_edge(cypher_parsestate *cpstate,
                                   cypher_relationship *rel,
                                   List **target_list, bool valid_label);
static Expr *transform_cypher_node(cypher_parsestate *cpstate,
                                   cypher_node *node, List **target_list,
                                   bool output_node, bool valid_label);
static bool match_check_valid_label(cypher_match *match,
                                    cypher_parsestate *cpstate);
static Node *make_vertex_expr(cypher_parsestate *cpstate,
                              ParseNamespaceItem *pnsi);
static Node *make_edge_expr(cypher_parsestate *cpstate,
                            ParseNamespaceItem *pnsi);
static Node *make_qual(cypher_parsestate *cpstate,
                           transform_entity *entity, char *name);
static TargetEntry *
transform_match_create_path_variable(cypher_parsestate *cpstate,
                                     cypher_path *path, List *entities);
static List *make_path_join_quals(cypher_parsestate *cpstate, List *entities);
static List *make_directed_edge_join_conditions(
    cypher_parsestate *cpstate, transform_entity *prev_entity,
    transform_entity *next_entity, Node *prev_qual, Node *next_qual,
    char *prev_node_label, char *next_node_label);
static List *join_to_entity(cypher_parsestate *cpstate,
                            transform_entity *entity, Node *qual,
                            enum transform_entity_join_side side);
static List *make_join_condition_for_edge(cypher_parsestate *cpstate,
                                          transform_entity *prev_edge,
                                          transform_entity *prev_node,
                                          transform_entity *entity,
                                          transform_entity *next_node,
                                          transform_entity *next_edge);
static List *make_edge_quals(cypher_parsestate *cpstate,
                             transform_entity *edge,
                             enum transform_entity_join_side side);
static A_Expr *filter_vertices_on_label_id(cypher_parsestate *cpstate,
                                           Node *id_field, char *label);
static Node *transform_map_to_ind(cypher_parsestate *cpstate,
                                  transform_entity *entity, cypher_map *map);
static List *transform_map_to_ind_recursive(cypher_parsestate *cpstate,
                                            transform_entity *entity,
                                            cypher_map *map,
                                            List *parent_fields);
static List *transform_map_to_ind_top_level(cypher_parsestate *cpstate,
                                            transform_entity *entity,
                                            cypher_map *map);
static Node *create_property_constraints(cypher_parsestate *cpstate,
                                         transform_entity *entity,
                                         Node *property_constraints,
                                         Node *prop_expr);
static TargetEntry *findTarget(List *targetList, char *resname);
static transform_entity *transform_VLE_edge_entity(cypher_parsestate *cpstate,
                                                   cypher_relationship *rel,
                                                   Query *query);
/* create clause */
static Query *transform_cypher_create(cypher_parsestate *cpstate,
                                      cypher_clause *clause);
static List *transform_cypher_create_pattern(cypher_parsestate *cpstate,
                                             Query *query, List *pattern);
static cypher_create_path *
transform_cypher_create_path(cypher_parsestate *cpstate, List **target_list,
                             cypher_path *cp);
static cypher_target_node *
transform_create_cypher_node(cypher_parsestate *cpstate, List **target_list,
                             cypher_node *node, bool has_edge);
static cypher_target_node *
transform_create_cypher_new_node(cypher_parsestate *cpstate,
                                 List **target_list, cypher_node *node);
static cypher_target_node *transform_create_cypher_existing_node(
    cypher_parsestate *cpstate, List **target_list, bool declared_in_current_clause,
    cypher_node *node);
static cypher_target_node *
transform_create_cypher_edge(cypher_parsestate *cpstate, List **target_list,
                             cypher_relationship *edge);
static Expr *cypher_create_properties(cypher_parsestate *cpstate,
                                      cypher_target_node *rel,
                                      Relation label_relation, Node *props,
                                      enum transform_entity_type type);
static Expr *add_volatile_wrapper(Expr *node);
static bool variable_exists(cypher_parsestate *cpstate, char *name);
static void add_volatile_wrapper_to_target_entry(List *target_list, int resno);
static int get_target_entry_resno(List *target_list, char *name);
static void handle_prev_clause(cypher_parsestate *cpstate, Query *query,
                               cypher_clause *clause, bool first_rte);
static TargetEntry *placeholder_target_entry(cypher_parsestate *cpstate,
                                             char *name);
static Query *transform_cypher_sub_pattern(cypher_parsestate *cpstate,
                                           cypher_clause *clause);
static Query *transform_cypher_sub_query(cypher_parsestate *cpstate,
                                         cypher_clause *clause);
/* set and remove clause */
static Query *transform_cypher_set(cypher_parsestate *cpstate,
                                   cypher_clause *clause);
static cypher_update_information *transform_cypher_set_item_list(cypher_parsestate *cpstate,
                                                                 List *set_item_list,
                                                                 Query *query);
static cypher_update_information *transform_cypher_remove_item_list(cypher_parsestate *cpstate,
                                                                    List *remove_item_list,
                                                                    Query *query);
/* delete */
static Query *transform_cypher_delete(cypher_parsestate *cpstate,
                                      cypher_clause *clause);
static List *transform_cypher_delete_item_list(cypher_parsestate *cpstate,
                                               List *delete_item_list,
                                               Query *query);
/* set operators */
static cypher_clause *make_cypher_clause(List *stmt);

static Query *transform_cypher_union(cypher_parsestate *cpstate,
                                     cypher_clause *clause);

static Node * transform_cypher_union_tree(cypher_parsestate *cpstate,
                                          cypher_clause *clause,
                                          bool isTopLevel,
                                          List **targetlist);

Query *cypher_parse_sub_analyze_union(cypher_clause *clause,
                                      cypher_parsestate *cpstate,
                                      CommonTableExpr *parentCTE,
                                      bool locked_from_parent,
                                      bool resolve_unknowns);
static void get_res_cols(ParseState *pstate, ParseNamespaceItem *l_pnsi,
                         ParseNamespaceItem *r_pnsi, List **res_colnames,
                         List **res_colvars);
/* unwind */
static Query *transform_cypher_unwind(cypher_parsestate *cpstate,
                                      cypher_clause *clause);

/* list comprehension */
static Query *transform_cypher_list_comprehension(cypher_parsestate *cpstate,
                                                  cypher_clause *clause);

/* merge */
static Query *transform_cypher_merge(cypher_parsestate *cpstate,
                                     cypher_clause *clause);
static cypher_create_path *
transform_merge_make_lateral_join(cypher_parsestate *cpstate, Query *query,
                                  cypher_clause *clause,
                                  cypher_clause *isolated_merge_clause);
static cypher_create_path *
transform_cypher_merge_path(cypher_parsestate *cpstate, List **target_list,
                            cypher_path *path);
static cypher_target_node *
transform_merge_cypher_edge(cypher_parsestate *cpstate, List **target_list,
                            cypher_relationship *edge);
static cypher_target_node *
transform_merge_cypher_node(cypher_parsestate *cpstate, List **target_list,
                            cypher_node *node, bool has_edge);
static Node *transform_clause_for_join(cypher_parsestate *cpstate,
                                       cypher_clause *clause,
                                       RangeTblEntry **rte,
                                       ParseNamespaceItem **nsitem,
                                       Alias* alias);
static cypher_clause *convert_merge_to_match(cypher_merge *merge);
static void
transform_cypher_merge_mark_tuple_position(cypher_parsestate *cpstate,
                                           List *target_list,
                                           cypher_create_path *path);
static cypher_target_node *get_referenced_variable(ParseState *pstate,
                                                   Node *node,
                                                   List *transformed_path);

/* call...[yield] */
static Query *transform_cypher_call_stmt(cypher_parsestate *cpstate,
                                         cypher_clause *clause);
static Query *transform_cypher_call_subquery(cypher_parsestate *cpstate,
                                             cypher_clause *clause);

/* transform */
#define PREV_CYPHER_CLAUSE_ALIAS AGE_DEFAULT_ALIAS_PREFIX"previous_cypher_clause"
#define CYPHER_OPT_RIGHT_ALIAS AGE_DEFAULT_ALIAS_PREFIX"cypher_optional_right"
#define transform_prev_cypher_clause(cpstate, prev_clause, add_rte_to_query) \
    transform_cypher_clause_as_subquery(cpstate, transform_cypher_clause, \
                                        prev_clause, NULL, add_rte_to_query)
static ParseNamespaceItem
*transform_cypher_clause_as_subquery(cypher_parsestate *cpstate,
                                     transform_method transform,
                                     cypher_clause *clause,
                                     Alias *alias,
                                     bool add_rte_to_query);
static Query *analyze_cypher_clause(transform_method transform,
                                    cypher_clause *clause,
                                    cypher_parsestate *parent_cpstate);
static List *transform_group_clause(cypher_parsestate *cpstate,
                                    List *grouplist, List **groupingSets,
                                    List **targetlist, List *sortClause,
                                    ParseExprKind exprKind);
static Node *flatten_grouping_sets(Node *expr, bool toplevel,
                                   bool *hasGroupingSets);
static Index transform_group_clause_expr(List **flatresult,
                                         Bitmapset *seen_local,
                                         cypher_parsestate *cpstate,
                                         Node *gexpr, List **targetlist,
                                         List *sortClause,
                                         ParseExprKind exprKind,
                                         bool toplevel);
static List *add_target_to_group_list(cypher_parsestate *cpstate,
                                      TargetEntry *tle, List *grouplist,
                                      List *targetlist, int location);
static void advance_transform_entities_to_next_clause(List *entities);

static ParseNamespaceItem *get_namespace_item(ParseState *pstate,
                                              RangeTblEntry *rte);
static List *make_target_list_from_join(ParseState *pstate,
                                        RangeTblEntry *rte);
static FuncExpr *make_clause_func_expr(char *function_name,
                                       Node *clause_information);
static void markRelsAsNulledBy(ParseState *pstate, Node *n, int jindex);

/* for VLE support */
static ParseNamespaceItem *transform_RangeFunction(cypher_parsestate *cpstate,
                                                   RangeFunction *r);
static Node *transform_from_clause_item(cypher_parsestate *cpstate, Node *n,
                                        RangeTblEntry **top_rte, int *top_rti,
                                        List **namespace);
static ParseNamespaceItem *append_VLE_Func_to_FromClause(cypher_parsestate *cpstate,
                                                         Node *n);
static void setNamespaceLateralState(List *namespace, bool lateral_only,
                                     bool lateral_ok);
static bool isa_special_VLE_case(cypher_path *path);

static ParseNamespaceItem *find_pnsi(cypher_parsestate *cpstate, char *varname);
static bool has_list_comp_or_subquery(Node *expr, void *context);
static bool clause_chain_has_dml(cypher_clause *clause);
static Node *make_false_where_clause(bool volatile_needed);

/*
 * Add required permissions to the RTEPermissionInfo for a relation.
 * Recursively searches through RTEs including subqueries.
 */
static bool
add_rte_permissions_recurse(List *rtable, List *rteperminfos,
                            Oid relid, AclMode permissions)
{
    ListCell *lc;

    /* First check the perminfos at this level */
    foreach(lc, rteperminfos)
    {
        RTEPermissionInfo *perminfo = lfirst(lc);

        if (perminfo->relid == relid)
        {
            perminfo->requiredPerms |= permissions;
            return true;
        }
    }

    /* Then recurse into subqueries */
    foreach(lc, rtable)
    {
        RangeTblEntry *rte = lfirst(lc);

        if (rte->rtekind == RTE_SUBQUERY && rte->subquery != NULL)
        {
            if (add_rte_permissions_recurse(rte->subquery->rtable,
                                            rte->subquery->rteperminfos,
                                            relid, permissions))
            {
                return true;
            }
        }
    }

    return false;
}

/*
 * Add required permissions to the RTEPermissionInfo for a relation.
 * Searches through p_rteperminfos and subqueries for a matching relOid
 * and adds the specified permissions to requiredPerms.
 */
static void
add_rte_permissions(ParseState *pstate, Oid relid, AclMode permissions)
{
    add_rte_permissions_recurse(pstate->p_rtable, pstate->p_rteperminfos,
                                relid, permissions);
}

/*
 * Add required permissions to the label table for a given entity variable.
 * Looks up the entity by variable name, extracts its label, and adds
 * the specified permissions to the corresponding RTEPermissionInfo.
 */
static void
add_entity_permissions(cypher_parsestate *cpstate, char *var_name,
                       AclMode permissions)
{
    ParseState *pstate = (ParseState *)cpstate;
    transform_entity *entity;
    char *label = NULL;
    Oid relid;

    entity = find_variable(cpstate, var_name);
    if (entity == NULL)
    {
        return;
    }

    if (entity->type == ENT_VERTEX)
    {
        label = entity->entity.node->label;
    }
    else if (entity->type == ENT_EDGE)
    {
        label = entity->entity.rel->label;
    }

    if (label == NULL)
    {
        return;
    }

    relid = get_label_relation(label, cpstate->graph_oid);
    if (OidIsValid(relid))
    {
        add_rte_permissions(pstate, relid, permissions);
    }
}

/*
 * transform a cypher_clause
 */
Query *transform_cypher_clause(cypher_parsestate *cpstate,
                               cypher_clause *clause)
{
    Node *self = clause->self;
    Query *result;

    /* examine the type of clause and call the transform logic for it */
    if (is_ag_node(self, cypher_return))
    {
        cypher_return *n = (cypher_return *) self;

        if (n->op == SETOP_NONE)
        {
            result = transform_cypher_return(cpstate, clause);
        }
        else if (n->op == SETOP_UNION)
        {
            result = transform_cypher_union(cpstate, clause);
        }
        else
        {
            ereport(ERROR, (errmsg_internal("unexpected Node for cypher_return")));
        }
    }
    else if (is_ag_node(self, cypher_with))
    {
        result = transform_cypher_with(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_match))
    {
        result = transform_cypher_match(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_create))
    {
        result = transform_cypher_create(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_set))
    {
        result = transform_cypher_set(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_delete))
    {
        result = transform_cypher_delete(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_merge))
    {
        result = transform_cypher_merge(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_sub_pattern))
    {
        result = transform_cypher_sub_pattern(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_sub_query))
    {
        result = transform_cypher_sub_query(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_unwind))
    {
        result = transform_cypher_unwind(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_call))
    {
        result = transform_cypher_call_stmt(cpstate, clause);
    }
    else if (is_ag_node(self, cypher_list_comprehension))
    {
        result = transform_cypher_list_comprehension(cpstate, clause);
    }
    else
    {
        ereport(ERROR, (errmsg_internal("unexpected Node for cypher_clause")));
    }

    result->querySource = QSRC_ORIGINAL;
    result->canSetTag = true;

    return result;
}

/*
 * Makes a cypher_clause from a list of nodes. Used by union
 * and subquery procedures to generate a subquery to transform.
 */

static cypher_clause *make_cypher_clause(List *stmt)
{
    cypher_clause *clause;
    ListCell *lc;

    /*
     * Since the first clause in stmt is the innermost subquery, the order of
     * the clauses is inverted.
     */
    clause = NULL;
    foreach (lc, stmt)
    {
        cypher_clause *next;

        next = palloc(sizeof(*next));
        next->next = NULL;
        next->self = lfirst(lc);
        next->prev = clause;

        if (clause != NULL)
        {
            clause->next = next;
        }
        clause = next;
    }
    return clause;
}

/*
 * transform_cypher_union -
 *    transforms a union tree, derived from postgresql's
 *    transformSetOperationStmt. A lot of the general logic is similar,
 *    with adjustments made for AGE.
 *
 * A union tree is just a return, but with UNION structure to it.
 * We must transform each leaf SELECT and build up a top-level Query
 * that contains the leaf SELECTs as subqueries in its rangetable.
 * The tree of unions is converted into the setOperations field of
 * the top-level Query.
 */

static Query *transform_cypher_union(cypher_parsestate *cpstate,
                                     cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    Query *qry = makeNode(Query);
    int leftmostRTI;
    Query *leftmostQuery;
    SetOperationStmt *cypher_union_statement;
    Node *skip = NULL; /* equivalent to postgres limitOffset */
    Node *limit = NULL; /* equivalent to postgres limitCount */
    List *order_by = NIL;
    Node *node;
    cypher_return *self = (cypher_return *)clause->self;
    ListCell *left_tlist, *lct, *lcm, *lcc;
    List *targetvars, *targetnames, *sv_namespace;
    int sv_rtable_length;
    int tllen;
    ParseNamespaceItem *nsitem;
    ParseNamespaceColumn *sortnscolumns;
    int sortcolindex;

    qry->commandType = CMD_SELECT;

    /*
     * Union is a node that should never have a previous node because
     * of where it is used in the parse logic. The query parts around it
     * are children located in larg or rarg. Something went wrong if the
     * previous clause field is not null.
     */
    if (clause->prev)
    {
        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                        errmsg("Union is a parent node, there are no previous"),
                        parser_errposition(&cpstate->pstate, 0)));
    }

    order_by = self->order_by;
    skip = self->skip;
    limit = self->limit;

    self->order_by = NIL;
    self->skip = NULL;
    self->limit = NULL;

    /*
     * Recursively transform the components of the tree.
     */
    cypher_union_statement = (SetOperationStmt *) transform_cypher_union_tree(cpstate,
                                                                clause, true, NULL);

    Assert(cypher_union_statement);
    qry->setOperations = (Node *) cypher_union_statement;

    /*
     * Re-find leftmost return (now it's a sub-query in rangetable)
     */
    node = cypher_union_statement->larg;
    while (node && IsA(node, SetOperationStmt))
    {
        node = ((SetOperationStmt *) node)->larg;
    }
    Assert(node && IsA(node, RangeTblRef));
    leftmostRTI = ((RangeTblRef *) node)->rtindex;
    leftmostQuery = rt_fetch(leftmostRTI, pstate->p_rtable)->subquery;
    Assert(leftmostQuery != NULL);

    /*
     * Generate dummy targetlist for outer query using column names of
     * leftmost return and common datatypes/collations of topmost set
     * operation.  Also make lists of the dummy vars and their names for use
     * in parsing ORDER BY.
     *
     * Note: we use leftmostRTI as the varno of the dummy variables. It
     * shouldn't matter too much which RT index they have, as long as they
     * have one that corresponds to a real RT entry; else funny things may
     * happen when the tree is mashed by rule rewriting.
     */
    qry->targetList = NIL;
    targetvars = NIL;
    targetnames = NIL;
    sortnscolumns = (ParseNamespaceColumn *)
            palloc0(list_length(cypher_union_statement->colTypes) * sizeof(ParseNamespaceColumn));
	sortcolindex = 0;

    forfour(lct, cypher_union_statement->colTypes,
            lcm, cypher_union_statement->colTypmods,
            lcc, cypher_union_statement->colCollations,
            left_tlist, leftmostQuery->targetList)
    {
        Oid colType = lfirst_oid(lct);
        int32 colTypmod = lfirst_int(lcm);
        Oid colCollation = lfirst_oid(lcc);
        TargetEntry *lefttle = (TargetEntry *) lfirst(left_tlist);
        char *colName;
        TargetEntry *tle;
        Var *var;

        Assert(!lefttle->resjunk);
        colName = pstrdup(lefttle->resname);
        var = makeVar(leftmostRTI,
                      lefttle->resno,
                      colType,
                      colTypmod,
                      colCollation,
                      0);
        var->location = exprLocation((Node *) lefttle->expr);
        tle = makeTargetEntry((Expr *) var,
                              (AttrNumber) pstate->p_next_resno++,
                               colName,
                               false);
        qry->targetList = lappend(qry->targetList, tle);
        targetvars = lappend(targetvars, var);
        targetnames = lappend(targetnames, makeString(colName));
        sortnscolumns[sortcolindex].p_varno = leftmostRTI;
        sortnscolumns[sortcolindex].p_varattno = lefttle->resno;
        sortnscolumns[sortcolindex].p_vartype = colType;
        sortnscolumns[sortcolindex].p_vartypmod = colTypmod;
        sortnscolumns[sortcolindex].p_varcollid = colCollation;
        sortnscolumns[sortcolindex].p_varnosyn = leftmostRTI;
        sortnscolumns[sortcolindex].p_varattnosyn = lefttle->resno;
        sortcolindex++;
    }

    /*
     * As a first step towards supporting sort clauses that are expressions
     * using the output columns, generate a namespace entry that makes the
     * output columns visible.  A Join RTE node is handy for this, since we
     * can easily control the Vars generated upon matches.
     *
     * Note: we don't yet do anything useful with such cases, but at least
     * "ORDER BY upper(foo)" will draw the right error message rather than
     * "foo not found".
     */
    sv_rtable_length = list_length(pstate->p_rtable);

    nsitem = addRangeTableEntryForJoin(pstate, targetnames, sortnscolumns,
                                       JOIN_INNER, 0, targetvars, NIL, NIL,
                                       NULL, NULL, false);

    sv_namespace = pstate->p_namespace;
    pstate->p_namespace = NIL;

    /* add jrte to column namespace only */
    addNSItemToQuery(pstate, nsitem, false, false, true);

    tllen = list_length(qry->targetList);

    qry->sortClause = transformSortClause(pstate,
                                          order_by,
                                          &qry->targetList,
                                          EXPR_KIND_ORDER_BY,
                                          false /* allow SQL92 rules */ );

    /* restore namespace, remove jrte from rtable */
    pstate->p_namespace = sv_namespace;
    pstate->p_rtable = list_truncate(pstate->p_rtable, sv_rtable_length);

    if (tllen != list_length(qry->targetList))
    {
        ereport(ERROR,
            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
             errmsg("invalid UNION ORDER BY clause"),
             errdetail("Only result column names can be used, not expressions or functions."),
             parser_errposition(pstate,
                                exprLocation(list_nth(qry->targetList, tllen)))));
    }

    qry->limitOffset = transform_cypher_limit(cpstate, skip,
                                              EXPR_KIND_OFFSET, "OFFSET");
    qry->limitCount = transform_cypher_limit(cpstate, limit,
                                              EXPR_KIND_LIMIT, "LIMIT");

    qry->rtable = pstate->p_rtable;
    qry->rteperminfos = pstate->p_rteperminfos;
    qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    qry->hasAggs = pstate->p_hasAggs;
    qry->hasSubLinks = pstate->p_hasSubLinks;

    assign_query_collations(pstate, qry);

    /* this must be done after collations, for reliable comparison of exprs */
    if (pstate->p_hasAggs ||
        qry->groupClause || qry->groupingSets || qry->havingQual)
    {
        parse_check_aggregates(pstate, qry);
    }

    return qry;

}

/*
 * transform_cypher_union_tree
 *      Recursively transform leaves and internal nodes of a set-op tree,
 *      derived from postgresql's transformSetOperationTree. A lot of
 *      the general logic is similar, with adjustments made for AGE.
 *
 * In addition to returning the transformed node, if targetlist isn't NULL
 * then we return a list of its non-resjunk TargetEntry nodes.  For a leaf
 * set-op node these are the actual targetlist entries; otherwise they are
 * dummy entries created to carry the type, typmod, collation, and location
 * (for error messages) of each output column of the set-op node.  This info
 * is needed only during the internal recursion of this function, so outside
 * callers pass NULL for targetlist.  Note: the reason for passing the
 * actual targetlist entries of a leaf node is so that upper levels can
 * replace UNKNOWN Consts with properly-coerced constants.
 */
static Node *
transform_cypher_union_tree(cypher_parsestate *cpstate, cypher_clause *clause,
                            bool isTopLevel, List **targetlist)
{
    bool isLeaf;

    ParseState *pstate = (ParseState *)cpstate;
    cypher_return *cmp;
    ParseNamespaceItem *pnsi;

    /* Guard against stack overflow due to overly complex set-expressions */
    check_stack_depth();

    if (IsA(clause, List))
    {
        clause = make_cypher_clause((List *)clause);
    }

    if (is_ag_node(clause->self, cypher_return))
    {
        cmp = (cypher_return *) clause->self;
    }
    else
    {
        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                errmsg("Cypher found an unsupported node"),
                parser_errposition(pstate, 0)));
    }


    if (cmp->op == SETOP_NONE)
    {
        Assert(cmp->larg == NULL && cmp->rarg == NULL);
        isLeaf = true;
    }
    else if (cmp->op == SETOP_UNION)
    {
        Assert(cmp->larg != NULL && cmp->rarg != NULL);
        if (cmp->order_by || cmp->limit || cmp->skip)
        {
            isLeaf = true;
        }
        else
        {
            isLeaf = false;
        }
    }
    else
    {
        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                errmsg("Cypher found an unsupported SETOP"),
                parser_errposition(pstate, 0)));
    }

    if (isLeaf)
    {
        /*process leaf return */
        Query *returnQuery;
        char returnName[32];
        RangeTblEntry *rte PG_USED_FOR_ASSERTS_ONLY;
        RangeTblRef *rtr;
        ListCell *tl;

        /*
         * Transform SelectStmt into a Query.
         *
         * This works the same as RETURN transformation normally would, except
         * that we prevent resolving unknown-type outputs as TEXT.  This does
         * not change the subquery's semantics since if the column type
         * matters semantically, it would have been resolved to something else
         * anyway.  Doing this lets us resolve such outputs using
         * select_common_type(), below.
         *
         * Note: previously transformed sub-queries don't affect the parsing
         * of this sub-query, because they are not in the toplevel pstate's
         * namespace list.
         */

        /*
         * Convert the List * that the grammar gave us to a cypher_clause.
         * cypher_analyze doesn't do this because the cypher_union clause
         * is hiding it.
         */

        returnQuery = cypher_parse_sub_analyze_union((cypher_clause *) clause, cpstate,
                                                     NULL, false, false);
        /*
         * Check for bogus references to Vars on the current query level (but
         * upper-level references are okay). Normally this can't happen
         * because the namespace will be empty, but it could happen if we are
         * inside a rule.
         */
        if (pstate->p_namespace)
        {
            if (contain_vars_of_level((Node *) returnQuery, 1))
            {
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                         errmsg("UNION member statement cannot refer to other relations of same query level"),
                         parser_errposition(pstate,
                                            locate_var_of_level((Node *) returnQuery, 1))));
            }
        }

        /*
         * Extract a list of the non-junk TLEs for upper-level processing.
         */

        /* mechanism to check for top level query list items here? */
        if (targetlist)
        {
            *targetlist = NIL;
            foreach(tl, returnQuery->targetList)
            {
                TargetEntry *tle = (TargetEntry *) lfirst(tl);

                if (!tle->resjunk)
                {
                    *targetlist = lappend(*targetlist, tle);
                }
            }
        }

        /*
         * Make the leaf query be a subquery in the top-level rangetable.
         */
        snprintf(returnName, sizeof(returnName), "*SELECT* %d ",
                 list_length(pstate->p_rtable) + 1);
        pnsi = addRangeTableEntryForSubquery(pstate,
                                             returnQuery,
                                             makeAlias(returnName, NIL),
                                             false,
                                             false);
        rte = pnsi->p_rte;
        rtr = makeNode(RangeTblRef);
        /* assume new rte is at end */
        rtr->rtindex = list_length(pstate->p_rtable);
        Assert(rte == rt_fetch(rtr->rtindex, pstate->p_rtable));
        return (Node *) rtr;
    }
    else /*is not a leaf */
    {
        /* Process an internal node (set operation node) */
        SetOperationStmt *op = makeNode(SetOperationStmt);
        List *ltargetlist;
        List *rtargetlist;
        ListCell *ltl;
        ListCell *rtl;
        cypher_return *self = (cypher_return *) clause->self;
        const char *context;

        context = "UNION";

        op->op = self->op;
        op->all = self->all_or_distinct;

        /*
         * Recursively transform the left child node.
         */
        op->larg = transform_cypher_union_tree(cpstate,
                                               (cypher_clause *) self->larg,
                                               false,
                                               &ltargetlist);

        /*
         * If we find ourselves processing a recursive CTE here something
         * went horribly wrong. That is an SQL construct with no parallel in
         * cypher.
         */
        if (isTopLevel &&
            pstate->p_parent_cte &&
            pstate->p_parent_cte->cterecursive)
        {
            ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                    errmsg("Cypher does not support recursive CTEs"),
                    parser_errposition(pstate, 0)));
        }

        /*
         * Recursively transform the right child node.
         */
        op->rarg = transform_cypher_union_tree(cpstate,
                                               (cypher_clause *) self->rarg,
                                               false,
                                               &rtargetlist);

        /*
         * Verify that the two children have the same number of non-junk
         * columns, and determine the types of the merged output columns.
         * If we are in a returnless subquery, we do not care about the columns
         * matching, because they are not relevant to the end result.
         */
        if (list_length(ltargetlist) != list_length(rtargetlist) &&
            self->returnless_union == false)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("each %s query must have the same number of columns",
                            context),
                     parser_errposition(pstate,
                                        exprLocation((Node *) rtargetlist))));
        }

        if (targetlist)
        {
            *targetlist = NIL;
        }

        op->colTypes = NIL;
        op->colTypmods = NIL;
        op->colCollations = NIL;
        op->groupClauses = NIL;

        forboth(ltl, ltargetlist, rtl, rtargetlist)
        {
            TargetEntry *ltle = (TargetEntry *) lfirst(ltl);
            TargetEntry *rtle = (TargetEntry *) lfirst(rtl);
            Node *lcolnode = (Node *) ltle->expr;
            Node *rcolnode = (Node *) rtle->expr;
            Oid lcoltype = exprType(lcolnode);
            Oid rcoltype = exprType(rcolnode);
            int32 lcoltypmod = exprTypmod(lcolnode);
            int32 rcoltypmod = exprTypmod(rcolnode);
            Node *bestexpr;
            int bestlocation;
            Oid rescoltype;
            int32 rescoltypmod;
            Oid rescolcoll;

            /* select common type, same as CASE et al */
            rescoltype = select_common_type(pstate,
                                            list_make2(lcolnode, rcolnode),
                                            context,
                                            &bestexpr);
            bestlocation = exprLocation(bestexpr);
            /* if same type and same typmod, use typmod; else default */
            if (lcoltype == rcoltype && lcoltypmod == rcoltypmod)
            {
                rescoltypmod = lcoltypmod;
            }
            else
            {
                rescoltypmod = -1;
            }

            /*
             * Verify the coercions are actually possible.  If not, we'd fail
             * later anyway, but we want to fail now while we have sufficient
             * context to produce an error cursor position.
             *
             * For all non-UNKNOWN-type cases, we verify coercibility but we
             * don't modify the child's expression, for fear of changing the
             * child query's semantics.
             *
             * If a child expression is an UNKNOWN-type Const or Param, we
             * want to replace it with the coerced expression.  This can only
             * happen when the child is a leaf set-op node.  It's safe to
             * replace the expression because if the child query's semantics
             * depended on the type of this output column, it'd have already
             * coerced the UNKNOWN to something else.  We want to do this
             * because (a) we want to verify that a Const is valid for the
             * target type, or resolve the actual type of an UNKNOWN Param,
             * and (b) we want to avoid unnecessary discrepancies between the
             * output type of the child query and the resolved target type.
             * Such a discrepancy would disable optimization in the planner.
             *
             * If it's some other UNKNOWN-type node, eg a Var, we do nothing
             * (knowing that coerce_to_common_type would fail).  The planner
             * is sometimes able to fold an UNKNOWN Var to a constant before
             * it has to coerce the type, so failing now would just break
             * cases that might work.
             */
            if (lcoltype != UNKNOWNOID)
            {
                lcolnode = coerce_to_common_type(pstate, lcolnode,
                                                 rescoltype, context);
            }
            else if (IsA(lcolnode, Const) || IsA(lcolnode, Param))
            {
                lcolnode = coerce_to_common_type(pstate, lcolnode,
                                                 rescoltype, context);
                ltle->expr = (Expr *) lcolnode;
            }

            if (rcoltype != UNKNOWNOID)
            {
                rcolnode = coerce_to_common_type(pstate, rcolnode,
                                                 rescoltype, context);
            }
            else if (IsA(rcolnode, Const) || IsA(rcolnode, Param))
            {
                rcolnode = coerce_to_common_type(pstate, rcolnode,
                                                 rescoltype, context);
                rtle->expr = (Expr *) rcolnode;
            }

            /*
             * Select common collation.  A common collation is required for
             * all set operators except UNION ALL; see SQL:2008 7.13 <query
             * expression> Syntax Rule 15c.  (If we fail to identify a common
             * collation for a UNION ALL column, the curCollations element
             * will be set to InvalidOid, which may result in a runtime error
             * if something at a higher query level wants to use the column's
             * collation.)
             */
            rescolcoll = select_common_collation(pstate,
                                                 list_make2(lcolnode, rcolnode),
                                                 (op->op == SETOP_UNION && op->all));

            /* emit results */
            op->colTypes = lappend_oid(op->colTypes, rescoltype);
            op->colTypmods = lappend_int(op->colTypmods, rescoltypmod);
            op->colCollations = lappend_oid(op->colCollations, rescolcoll);

            /*
             * For all cases except UNION ALL, identify the grouping operators
             * (and, if available, sorting operators) that will be used to
             * eliminate duplicates.
             */
            if (op->op != SETOP_UNION || !op->all)
            {
                SortGroupClause *grpcl = makeNode(SortGroupClause);
                Oid sortop;
                Oid eqop;
                bool hashable = false;
                ParseCallbackState pcbstate;

                setup_parser_errposition_callback(&pcbstate, pstate,
                                                  bestlocation);

                /*
                 * determine the eqop and optional sortop
                 *
                 * NOTE: for UNION, we set hashable to false and pass a NULL to
                 * isHashable in get_sort_group_operators to prevent a logic error
                 * where UNION fails to exclude duplicate results.
                 *
                 */
                get_sort_group_operators(rescoltype,
                                         false, true, false,
                                         &sortop, &eqop, NULL,
                                         NULL);

                cancel_parser_errposition_callback(&pcbstate);

                /* we don't have a tlist yet, so can't assign sortgrouprefs */
                grpcl->tleSortGroupRef = 0;
                grpcl->eqop = eqop;
                grpcl->sortop = sortop;
                grpcl->nulls_first = false; /* OK with or without sortop */
                grpcl->hashable = hashable;

                op->groupClauses = lappend(op->groupClauses, grpcl);
            }

            /*
             * Construct a dummy tlist entry to return.  We use a SetToDefault
             * node for the expression, since it carries exactly the fields
             * needed, but any other expression node type would do as well.
             */
            if (targetlist)
            {
                SetToDefault *rescolnode = makeNode(SetToDefault);
                TargetEntry *restle;

                rescolnode->typeId = rescoltype;
                rescolnode->typeMod = rescoltypmod;
                rescolnode->collation = rescolcoll;
                rescolnode->location = bestlocation;
                restle = makeTargetEntry((Expr *) rescolnode,
                                         0, /* no need to set resno */
                                         NULL,
                                         false);
                *targetlist = lappend(*targetlist, restle);
            }
        }

        return (Node *)op;
    }/* end else (is not leaf) */
}

/*
 * Function that takes a cypher call and returns the yielded result
 * This function also catches some cases that should fail that could not
 * be picked up by the grammar. transform_cypher_call_subquery handles the
 * call transformation itself.
 */
static Query *transform_cypher_call_stmt(cypher_parsestate *cpstate,
                                         cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_call *self = (cypher_call *)clause->self;

    /* CALL [YIELD] -- the most simple call */
    if (!clause->prev && !clause->next)
    {
        /* Error check for WHERE clause after YIELD without RETURN */
        if (self->where)
        {
            Assert(self->yield_items);

            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("Cannot use standalone CALL with WHERE"),
                     errhint("Instead use `CALL ... WITH * WHERE ... RETURN *`"),
                     parser_errposition(pstate,
                                        exprLocation((Node *) self->where))));
        }

        return transform_cypher_call_subquery(cpstate, clause);
    }
    else /* subqueries */
    {
        if (!self->yield_items)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("Procedure call inside a query does not support naming results implicitly"),
                     errhint("Name explicitly using `YIELD` instead"),
                     parser_errposition(pstate,
                                        exprLocation((Node *) self))));
        }
        Assert(self->yield_items);

        if (!clause->next)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("Query cannot conclude with CALL"),
                     errhint("Must be RETURN or an update clause"),
                     parser_errposition(pstate,
                                        exprLocation((Node *) self))));
        }

        return transform_cypher_clause_with_where(cpstate,
                                                  transform_cypher_call_subquery,
                                                  clause, self->where);
    }

    return NULL;
}

/*
 * Helper routine for transform_cypher_call_stmt. This routine transforms the
 * call statement and handles the YIELD clause.
 */
static Query *transform_cypher_call_subquery(cypher_parsestate *cpstate,
                                             cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    ParseState *p_child_parse_state = make_parsestate(NULL);
    cypher_call *self = (cypher_call *)clause->self;
    Query *query;
    char *colName;
    FuncExpr *node = NULL;
    TargetEntry *tle;

    Expr *where_qual = NULL;

    query = makeNode(Query);
    query->commandType = CMD_SELECT;

    if (clause->prev)
    {
        /* we want to retain all previous range table entries */
        handle_prev_clause(cpstate, query, clause->prev, false);
    }

    /* transform the funccall and store it in a funcexpr node */
    node = castNode( FuncExpr, transform_cypher_expr(cpstate, (Node *) self->funccall,
                                                     EXPR_KIND_FROM_FUNCTION));

    /* retrieve the column name from funccall */
    colName = strVal(llast(self->funccall->funcname));

    /* make a targetentry from the funcexpr node */
    tle = makeTargetEntry((Expr *) node,
                          (AttrNumber) p_child_parse_state->p_next_resno++,
                           colName,
                           false);

     /* if there are yield items, we need to check them */
    if (self->yield_items)
    {
        List *yield_targetList;
        ListCell *lc;

        yield_targetList = list_make1(tle);

        foreach (lc, self->yield_items)
        {
            ResTarget *target = NULL;
            ColumnRef *var = NULL;
            TargetEntry *yielded_tle = NULL;

            target = (ResTarget *) lfirst(lc);

            if (!IsA(target->val, ColumnRef))
            {
                ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                errmsg("YIELD item must be ColumnRef"),
                                parser_errposition(&cpstate->pstate, 0)));
            }

            var = (ColumnRef *) target->val;

            /* check if the restarget variable exists in the yield_targetList*/
            if (findTarget(yield_targetList, strVal(linitial(var->fields))) != NULL)
            {
                /* check if an alias exists. if one does, we check if it is
                   already declared in the targetlist */
                if (target->name)
                {
                    if (findTarget(query->targetList, target->name) != NULL)
                    {
                        ereport(ERROR,
                                (errcode(ERRCODE_DUPLICATE_ALIAS),
                                        errmsg("duplicate variable \"%s\"", target->name),
                                        parser_errposition((ParseState *) cpstate, exprLocation((Node *) target))));
                    }
                    else
                    {
                        yielded_tle = makeTargetEntry((Expr *) node,
                                                      (AttrNumber) pstate->p_next_resno++,
                                                       target->name,
                                                       false);
                        query->targetList = lappend(query->targetList, yielded_tle);
                    }
                }
                else/* if there is no alias, we check if the variable is already declared */
                {
                    if (findTarget(query->targetList, strVal(linitial(var->fields))) != NULL)
                    {
                        ereport(ERROR,
                                (errcode(ERRCODE_DUPLICATE_ALIAS),
                                        errmsg("duplicate variable \"%s\"", colName),
                                        parser_errposition((ParseState *) cpstate, exprLocation((Node *) target))));
                    }
                    else
                    {
                        yielded_tle = makeTargetEntry((Expr *) node,
                                                      (AttrNumber) pstate->p_next_resno++,
                                                       colName,
                                                       false);
                        query->targetList = lappend(query->targetList, yielded_tle);
                    }
                }
            }
            else
            {
                /* if the yield_item is not found and we return an error */
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                         errmsg("Unknown CALL output"),
                         parser_errposition(pstate, exprLocation((Node *) target))));
            }
        }
    }
    else /* if there are no yield items this must be a solo call */
    {
        tle = makeTargetEntry((Expr *) node,
                                    (AttrNumber) pstate->p_next_resno++,
                                     colName,
                                     false);
        query->targetList =  list_make1(tle);
    }



    markTargetListOrigins(pstate, query->targetList);

    query->rtable = cpstate->pstate.p_rtable;
    query->rteperminfos = cpstate->pstate.p_rteperminfos;
    query->jointree = makeFromExpr(cpstate->pstate.p_joinlist, (Node *)where_qual);
    query->hasAggs = pstate->p_hasAggs;
    query->hasSubLinks = pstate->p_hasSubLinks;

    assign_query_collations(pstate, query);

    /* this must be done after collations, for reliable comparison of exprs */
    if (pstate->p_hasAggs ||
        query->groupClause || query->groupingSets || query->havingQual)
    {
        parse_check_aggregates(pstate, query);
    }

    free_parsestate(p_child_parse_state);

    return query;
}

/*
 * Transform the Delete clause. Creates a _cypher_delete_clause
 * and passes the necessary information that is needed in the
 * execution phase.
 */
static Query *transform_cypher_delete(cypher_parsestate *cpstate,
                                      cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_delete *self = (cypher_delete *)clause->self;
    Query *query;
    TargetEntry *tle;
    FuncExpr *func_expr;

    cypher_delete_information *delete_data;

    delete_data = make_ag_node(cypher_delete_information);

    query = makeNode(Query);
    query->commandType = CMD_SELECT;
    query->targetList = NIL;

    if (!clause->prev)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("DELETE cannot be the first clause in a Cypher query"),
                 parser_errposition(pstate, self->location)));
    }
    else
    {
        handle_prev_clause(cpstate, query, clause->prev, true);
    }

    delete_data->delete_items = transform_cypher_delete_item_list(cpstate,
                                                                  self->exprs,
                                                                  query);
    delete_data->graph_name = cpstate->graph_name;
    delete_data->graph_oid = cpstate->graph_oid;
    delete_data->detach = self->detach;

    if (!clause->next)
    {
        delete_data->flags |= CYPHER_CLAUSE_FLAG_TERMINAL;
    }

    func_expr = make_clause_func_expr(DELETE_CLAUSE_FUNCTION_NAME,
                                      (Node *)delete_data);

    /* Create the target entry */
    tle = makeTargetEntry((Expr *)func_expr, pstate->p_next_resno++,
                          AGE_VARNAME_DELETE_CLAUSE, false);
    query->targetList = lappend(query->targetList, tle);

    query->rtable = pstate->p_rtable;
    query->rteperminfos = pstate->p_rteperminfos;
    query->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    query->hasAggs = pstate->p_hasAggs;
    query->hasSubLinks = pstate->p_hasSubLinks;

    return query;
}

/*
 * transform_cypher_unwind
 *      It contains logic to convert the form of an array into a row. Here, we
 *      are simply calling `age_unnest` function, and the actual transformation
 *      is handled by `age_unnest` function.
 */
static Query *transform_cypher_unwind(cypher_parsestate *cpstate,
                                      cypher_clause *clause)
{
    ParseState *pstate = (ParseState *) cpstate;
    cypher_unwind *self = (cypher_unwind *) clause->self;
    int target_syntax_loc;
    Query *query;
    Node *expr;
    FuncCall *unwind;
    ParseExprKind old_expr_kind;
    Node *funcexpr;
    TargetEntry *te;
    ParseNamespaceItem *pnsi;

    query = makeNode(Query);
    query->commandType = CMD_SELECT;

    if (clause->prev)
    {
        int rtindex;

        pnsi = transform_prev_cypher_clause(cpstate, clause->prev, true);
        rtindex = list_length(pstate->p_rtable);
        /* rte is the first RangeTblEntry in pstate */
        if (rtindex != 1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("invalid value for rtindex")));
        }

        query->targetList = expandNSItemAttrs(pstate, pnsi, 0, true, -1);
    }

    target_syntax_loc = exprLocation((const Node *) self->target);

    if (findTarget(query->targetList, self->target->name) != NULL)
    {
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("duplicate variable \"%s\"", self->target->name),
                        parser_errposition((ParseState *) cpstate,
                                           target_syntax_loc)));
    }

    expr = transform_cypher_expr(cpstate, self->target->val,
                                 EXPR_KIND_SELECT_TARGET);

    if (nodeTag(expr) == T_Aggref)
    {
        ereport(ERROR, errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                errmsg("Invalid use of aggregation in this context"),
                parser_errposition(pstate, self->target->location));
    }

    unwind = makeFuncCall(list_make1(makeString("age_unnest")), NIL,
                          COERCE_SQL_SYNTAX, -1);

    old_expr_kind = pstate->p_expr_kind;
    pstate->p_expr_kind = EXPR_KIND_SELECT_TARGET;
    funcexpr = ParseFuncOrColumn(pstate, unwind->funcname,
                                 list_make1(expr),
                                 pstate->p_last_srf, unwind, false,
                                 target_syntax_loc);

    pstate->p_expr_kind = old_expr_kind;

    te = makeTargetEntry((Expr *) funcexpr,
                         (AttrNumber) pstate->p_next_resno++,
                         self->target->name, false);

    query->targetList = lappend(query->targetList, te);
    query->rtable = pstate->p_rtable;
    query->rteperminfos = pstate->p_rteperminfos;
    query->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    query->hasTargetSRFs = pstate->p_hasTargetSRFs;
    query->hasAggs = pstate->p_hasAggs;
    query->hasSubLinks = pstate->p_hasSubLinks;

    assign_query_collations(pstate, query);

    return query;
}

/*
 * [i IN u WHERE i<2 | i^2]
 *
 *   |    |    |    |    |
 *  \|/  \|/  \|/  \|/  \|/
 *
 * SELECT i^2 FROM age_unnest(u) AS i WHERE i>2;
 */
static Query *transform_cypher_list_comprehension(cypher_parsestate *cpstate,
                                                  cypher_clause *clause)
{
    Query *query;
    RangeFunction *rf;
    cypher_list_comprehension *list_comp = (cypher_list_comprehension *) clause->self;
    FuncCall *func_call;
    Node *return_expr, *qual, *n;
    RangeTblEntry *rte = NULL;
    int rtindex;
    List *namespace = NULL;
    TargetEntry *te;
    cypher_parsestate *child_cpstate = make_cypher_parsestate(cpstate);
    ParseState *child_pstate = (ParseState *) child_cpstate;

    query = makeNode(Query);
    query->commandType = CMD_SELECT;

    func_call = makeFuncCall(list_make1(makeString("unnest")),
                             list_make1(list_comp->expr),
                             COERCE_SQL_SYNTAX, -1);

    rf = makeNode(RangeFunction);
    rf->lateral = false;
    rf->ordinality = false;
    rf->is_rowsfrom = false;
    rf->functions = list_make1(list_make2((Node *) func_call, NIL));
    rf->alias = makeAlias(list_comp->varname, NIL);
    rf->coldeflist = NIL;

    n = transform_from_clause_item(child_cpstate, (Node *) rf,
                                   &rte, &rtindex, &namespace);
    checkNameSpaceConflicts(child_pstate, child_pstate->p_namespace, namespace);
    child_pstate->p_joinlist = lappend(child_pstate->p_joinlist, n);
    child_pstate->p_namespace = list_concat(child_pstate->p_namespace, namespace);

    /* make all namespace items unconditionally visible */
    setNamespaceLateralState(child_pstate->p_namespace, false, true);

    return_expr = transform_cypher_expr(child_cpstate, list_comp->mapping_expr,
                                        EXPR_KIND_SELECT_TARGET);
    
    te = makeTargetEntry((Expr *) return_expr,
                         (AttrNumber) child_pstate->p_next_resno++,
                         list_comp->varname, false);

    qual = transform_cypher_expr(child_cpstate, list_comp->where,
                                 EXPR_KIND_WHERE);
    if (qual)
    {
        qual = coerce_to_boolean(child_pstate, qual, "WHERE");
    }

    query->targetList = lappend(query->targetList, te);
    query->jointree = makeFromExpr(child_pstate->p_joinlist, (Node *) qual);
    query->rtable = child_pstate->p_rtable;
    query->rteperminfos = child_pstate->p_rteperminfos;
    query->hasAggs = child_pstate->p_hasAggs;
    query->hasSubLinks = child_pstate->p_hasSubLinks;
    query->hasTargetSRFs = child_pstate->p_hasTargetSRFs;

    assign_query_collations(child_pstate, query);

    if (child_pstate->p_hasAggs ||
        query->groupClause || query->groupingSets || query->havingQual)
    {
        parse_check_aggregates(child_pstate, query);
    }

    free_cypher_parsestate(child_cpstate);

    return query;
}

/*
 * Iterate through the list of items to delete and extract the variable name.
 * Then find the resno that the variable name belongs to.
 */
static List *transform_cypher_delete_item_list(cypher_parsestate *cpstate,
                                               List *delete_item_list,
                                               Query *query)
{
    ParseState *pstate = (ParseState *)cpstate;
    List *items = NIL;
    ListCell *lc;

    foreach(lc, delete_item_list)
    {
        Node *expr = lfirst(lc);
        ColumnRef *col;
        String *val;
        Integer *pos;
        int resno;

        cypher_delete_item *item = make_ag_node(cypher_delete_item);

        if (!IsA(expr, ColumnRef))
        {
            ereport(ERROR,
                    (errmsg_internal("unexpected Node for cypher_clause")));
        }

        col = (ColumnRef *)expr;

        if (list_length(col->fields) != 1)
        {
            ereport(ERROR,
                    (errmsg_internal("unexpected Node for cypher_clause")));
        }

        val = linitial(col->fields);

        if (!IsA(val, String))
        {
            ereport(ERROR,
                    (errmsg_internal("unexpected Node for cypher_clause")));
        }

        resno = get_target_entry_resno(query->targetList, val->sval);
        if (resno == -1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                     errmsg("undefined reference to variable %s in DELETE clause",
                            val->sval),
                     parser_errposition(pstate, col->location)));
        }

        /* Add ACL_DELETE permission to the entity's label table */
        add_entity_permissions(cpstate, val->sval, ACL_DELETE);

        add_volatile_wrapper_to_target_entry(query->targetList, resno);

        pos = makeInteger(resno);

        item->var_name = val->sval;
        item->entity_position = pos;

        items = lappend(items, item);
    }

    return items;
}

static Query *transform_cypher_set(cypher_parsestate *cpstate,
                                   cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_set *self = (cypher_set *)clause->self;
    Query *query;
    cypher_update_information *set_items_target_list;
    TargetEntry *tle;
    FuncExpr *func_expr;
    char *clause_name;

    query = makeNode(Query);
    query->commandType = CMD_SELECT;
    query->targetList = NIL;

    if (self->is_remove == true)
    {
        clause_name = UPDATE_CLAUSE_REMOVE;
    }
    else
    {
        clause_name = UPDATE_CLAUSE_SET;
    }

    if (!clause->prev)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("%s cannot be the first clause in a Cypher query",
                        clause_name),
                 parser_errposition(pstate, self->location)));
    }
    else
    {
        handle_prev_clause(cpstate, query, clause->prev, true);
    }

    if (self->is_remove == true)
    {
        set_items_target_list = transform_cypher_remove_item_list(cpstate,
                                                                  self->items,
                                                                  query);
    }
    else
    {
        set_items_target_list = transform_cypher_set_item_list(cpstate,
                                                               self->items,
                                                               query);
    }

    set_items_target_list->clause_name = clause_name;
    set_items_target_list->graph_name = cpstate->graph_name;

    if (!clause->next)
    {
        set_items_target_list->flags |= CYPHER_CLAUSE_FLAG_TERMINAL;
    }

    func_expr = make_clause_func_expr(SET_CLAUSE_FUNCTION_NAME,
                                      (Node *)set_items_target_list);

    /* Create the target entry */
    tle = makeTargetEntry((Expr *)func_expr, pstate->p_next_resno++,
                          AGE_VARNAME_SET_CLAUSE, false);
    query->targetList = lappend(query->targetList, tle);

    query->rtable = pstate->p_rtable;
    query->rteperminfos = pstate->p_rteperminfos;
    query->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    query->hasAggs = pstate->p_hasAggs;
    query->hasSubLinks = pstate->p_hasSubLinks;

    return query;
}

cypher_update_information *transform_cypher_remove_item_list(
    cypher_parsestate *cpstate, List *remove_item_list, Query *query)
{
    ParseState *pstate = (ParseState *)cpstate;
    ListCell *li;
    cypher_update_information *info = make_ag_node(cypher_update_information);

    info->set_items = NIL;
    info->flags = 0;

    foreach (li, remove_item_list)
    {
        cypher_set_item *set_item = lfirst(li);
        cypher_update_item *item;
        ColumnRef *ref;
        A_Indirection *ind;
        char *variable_name, *property_name;
        String *property_node, *variable_node;

        item = make_ag_node(cypher_update_item);

        if (!is_ag_node(lfirst(li), cypher_set_item))
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("unexpected node in cypher update list")));
        }

        if (set_item->is_add)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("REMOVE clause does not support adding properties from maps"),
                     parser_errposition(pstate, set_item->location)));
        }
        set_item->is_add = false;

        item->remove_item = true;


        if (!IsA(set_item->prop, A_Indirection))
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("REMOVE clause must be in the format: REMOVE variable.property_name"),
                     parser_errposition(pstate, set_item->location)));
        }

        ind = (A_Indirection *)set_item->prop;

        /* extract variable name */
        if (!IsA(ind->arg, ColumnRef))
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("REMOVE clause must be in the format: REMOVE variable.property_name"),
                     parser_errposition(pstate, set_item->location)));
        }

        ref = (ColumnRef *)ind->arg;

        variable_node = linitial(ref->fields);

        variable_name = variable_node->sval;
        item->var_name = variable_name;

        item->entity_position = get_target_entry_resno(query->targetList,
                                                       variable_name);
        if (item->entity_position == -1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                     errmsg("undefined reference to variable %s in REMOVE clause",
                            variable_name),
                     parser_errposition(pstate, set_item->location)));
        }

        /* Add ACL_UPDATE permission to the entity's label table */
        add_entity_permissions(cpstate, variable_name, ACL_UPDATE);

        add_volatile_wrapper_to_target_entry(query->targetList,
                                             item->entity_position);

        /* extract property name */
        if (list_length(ind->indirection) != 1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("REMOVE clause must be in the format: REMOVE variable.property_name"),
                     parser_errposition(pstate, set_item->location)));
        }

        property_node = linitial(ind->indirection);

        if (!IsA(property_node, String))
        {
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                     errmsg("REMOVE clause expects a property name"),
                     parser_errposition(pstate, set_item->location)));
        }
        property_name = property_node->sval;
        item->prop_name = property_name;

        info->set_items = lappend(info->set_items, item);
    }

    return info;
}


cypher_update_information *transform_cypher_set_item_list(
    cypher_parsestate *cpstate, List *set_item_list, Query *query)
{
    ParseState *pstate = (ParseState *)cpstate;
    ListCell *li;
    cypher_update_information *info = make_ag_node(cypher_update_information);

    info->set_items = NIL;
    info->flags = 0;

    foreach (li, set_item_list)
    {
        cypher_set_item *set_item = lfirst(li);
        TargetEntry *target_item;
        cypher_update_item *item;
        ColumnRef *ref;
        A_Indirection *ind;
        char *variable_name, *property_name;
        String *property_node, *variable_node;
        int is_entire_prop_update = 0; /* true if a map is assigned to variable */

        /* LHS of set_item must be a variable or an indirection. */
        if (IsA(set_item->prop, ColumnRef))
        {
            /*
             * A variable can only be assigned a map, a function call that
             * evaluates to a map, or a variable.
             *
             * In case of a function call, whether it actually evaluates to
             * map is checked in the execution stage.
             */
            if (!is_ag_node(set_item->expr, cypher_map) &&
                !IsA(set_item->expr, FuncCall) &&
                !IsA(set_item->expr, ColumnRef))
            {
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("SET clause expects a map"),
                         parser_errposition(pstate, set_item->location)));
            }

            is_entire_prop_update = 1;

            /*
             * In case of a variable, it is wrapped as an argument to
             * the 'properties' function.
             */
            if (IsA(set_item->expr, ColumnRef))
            {
                List *qualified_name, *args;

                qualified_name = list_make2(makeString("ag_catalog"),
                                            makeString("age_properties"));
                args = list_make1(set_item->expr);
                set_item->expr = (Node *)makeFuncCall(qualified_name, args,
                                                      COERCE_SQL_SYNTAX, -1);
            }
        }
        else if (!IsA(set_item->prop, A_Indirection))
        {
            ereport(ERROR, (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                            errmsg("SET clause expects a variable name"),
                            parser_errposition(pstate, set_item->location)));
        }

        item = make_ag_node(cypher_update_item);

        if (!is_ag_node(lfirst(li), cypher_set_item))
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("unexpected node in cypher update list")));
        }

        item->remove_item = false;

        /* set variable, is_add and extract property name */
        if (is_entire_prop_update)
        {
            ref = (ColumnRef *)set_item->prop;
            item->is_add = set_item->is_add;
            item->prop_name = NULL;
        }
        else
        {
            ind = (A_Indirection *)set_item->prop;
            ref = (ColumnRef *)ind->arg;

            if (set_item->is_add)
            {
                ereport(
                    ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg(
                         "SET clause does not yet support incrementing a specific property"),
                     parser_errposition(pstate, set_item->location)));
            }
            set_item->is_add = false;

            /* extract property name */
            if (list_length(ind->indirection) != 1)
            {
                ereport(
                    ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("SET clause doesn't not support updating maps or lists in a property"),
                     parser_errposition(pstate, set_item->location)));
            }

            property_node = linitial(ind->indirection);
            if (!IsA(property_node, String))
            {
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                         errmsg("SET clause expects a property name"),
                         parser_errposition(pstate, set_item->location)));
            }

            property_name = property_node->sval;
            item->prop_name = property_name;
        }

        /* extract variable name */
        variable_node = linitial(ref->fields);
        if (!IsA(variable_node, String))
        {
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                     errmsg("SET clause expects a variable name"),
                     parser_errposition(pstate, set_item->location)));
        }

        variable_name = variable_node->sval;
        item->var_name = variable_name;

        item->entity_position = get_target_entry_resno(query->targetList,
                                                       variable_name);
        if (item->entity_position == -1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                     errmsg("undefined reference to variable %s in SET clause",
                            variable_name),
                            parser_errposition(pstate, set_item->location)));
        }

        /* Add ACL_UPDATE permission to the entity's label table */
        add_entity_permissions(cpstate, variable_name, ACL_UPDATE);

        add_volatile_wrapper_to_target_entry(query->targetList,
                                             item->entity_position);

        /* set keep_null property */
        if (is_ag_node(set_item->expr, cypher_map))
        {
            ((cypher_map*)set_item->expr)->keep_null = set_item->is_add;
        }

        /*
         * Create target entry for the new property value.
         *
         * We use a hidden variable name (AGE_VARNAME_SET_VALUE) for the
         * SET expression value to prevent column name conflicts. This is
         * necessary when the same variable is used on both the LHS and RHS
         * of a SET clause (e.g., SET n.prop = n). Without this, the column
         * name derived from the expression (e.g., "n") would duplicate the
         * existing column name from the MATCH clause, causing a "column
         * reference is ambiguous" error in subsequent clauses like RETURN.
         *
         * The hidden variable name will be filtered out by expand_pnsi_attrs
         * when the targetlist is expanded for subsequent clauses.
         */
        item->prop_position = (AttrNumber)pstate->p_next_resno;
        target_item = transform_cypher_item(cpstate, set_item->expr, NULL,
                                            EXPR_KIND_SELECT_TARGET,
                                            AGE_VARNAME_SET_VALUE,
                                            false);

        if (nodeTag(target_item->expr) == T_Aggref)
        {
            ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                    errmsg("Invalid use of aggregation in this context"),
                    parser_errposition(pstate, set_item->location)));
        }

        target_item->expr = add_volatile_wrapper(target_item->expr);

        query->targetList = lappend(query->targetList, target_item);
        info->set_items = lappend(info->set_items, item);
    }

    return info;
}

/* from PG's static helper function */
static Node *flatten_grouping_sets(Node *expr, bool toplevel,
                                   bool *hasGroupingSets)
{
    /* just in case of pathological input */
    check_stack_depth();

    if (expr == (Node *) NIL)
    {
        return (Node *) NIL;
    }

    switch (expr->type)
    {
        case T_RowExpr:
        {
            RowExpr *r = (RowExpr *) expr;

            if (r->row_format == COERCE_IMPLICIT_CAST)
            {
                return flatten_grouping_sets((Node *) r->args, false, NULL);
            }
            break;
        }
        case T_GroupingSet:
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("flattening of GroupingSet is not implemented")));
            break;
        case T_List:
        {
            List *result = NIL;
            ListCell *l;

            foreach(l, (List *) expr)
            {
                Node *n = NULL;

                n = flatten_grouping_sets(lfirst(l), toplevel, hasGroupingSets);

                if (n != (Node *) NIL)
                {
                    if (IsA(n, List))
                    {
                        result = list_concat(result, (List *) n);
                    }
                    else
                    {
                        result = lappend(result, n);
                    }
                }
            }
            return (Node *) result;
        }
        default:
            break;
    }
    return expr;
}

/* from PG's addTargetToGroupList */
static List *add_target_to_group_list(cypher_parsestate *cpstate,
                                      TargetEntry *tle, List *grouplist,
                                      List *targetlist, int location)
{
    ParseState *pstate = &cpstate->pstate;
    Oid restype = exprType((Node *) tle->expr);

    /* if tlist item is an UNKNOWN literal, change it to TEXT */
    if (restype == UNKNOWNOID)
    {
        tle->expr = (Expr *) coerce_type(pstate, (Node *) tle->expr, restype,
                                         TEXTOID, -1, COERCION_IMPLICIT,
                                         COERCE_IMPLICIT_CAST, -1);
        restype = TEXTOID;
    }

    /* avoid making duplicate grouplist entries */
    if (!targetIsInSortList(tle, InvalidOid, grouplist))
    {
        SortGroupClause *grpcl = makeNode(SortGroupClause);
        Oid sortop;
        Oid eqop;
        bool hashable;
        ParseCallbackState pcbstate;

        setup_parser_errposition_callback(&pcbstate, pstate, location);

        /* determine the eqop and optional sortop */
        get_sort_group_operators(restype, false, true, false, &sortop, &eqop,
                                 NULL, &hashable);

        cancel_parser_errposition_callback(&pcbstate);

        grpcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
        grpcl->eqop = eqop;
        grpcl->sortop = sortop;
        grpcl->nulls_first = false; /* OK with or without sortop */
        grpcl->hashable = hashable;

        grouplist = lappend(grouplist, grpcl);
    }

    return grouplist;
}

/* from PG's transformGroupClauseExpr */
static Index transform_group_clause_expr(List **flatresult,
                                         Bitmapset *seen_local,
                                         cypher_parsestate *cpstate,
                                         Node *gexpr, List **targetlist,
                                         List *sortClause,
                                         ParseExprKind exprKind, bool toplevel)
{
    TargetEntry *tle = NULL;
    bool found = false;

    tle = find_target_list_entry(cpstate, gexpr, targetlist, exprKind);

    if (tle->ressortgroupref > 0)
    {
        ListCell *sl;

        /*
         * Eliminate duplicates (GROUP BY x, x) but only at local level.
         * (Duplicates in grouping sets can affect the number of returned
         * rows, so can't be dropped indiscriminately.)
         *
         * Since we don't care about anything except the sortgroupref, we can
         * use a bitmapset rather than scanning lists.
         */
        if (bms_is_member(tle->ressortgroupref, seen_local))
        {
            return 0;
        }

        /*
         * If we're already in the flat clause list, we don't need to consider
         * adding ourselves again.
         */
        found = targetIsInSortList(tle, InvalidOid, *flatresult);
        if (found)
        {
            return tle->ressortgroupref;
        }

        /*
         * If the GROUP BY tlist entry also appears in ORDER BY, copy operator
         * info from the (first) matching ORDER BY item.  This means that if
         * you write something like "GROUP BY foo ORDER BY foo USING <<<", the
         * GROUP BY operation silently takes on the equality semantics implied
         * by the ORDER BY.  There are two reasons to do this: it improves the
         * odds that we can implement both GROUP BY and ORDER BY with a single
         * sort step, and it allows the user to choose the equality semantics
         * used by GROUP BY, should she be working with a datatype that has
         * more than one equality operator.
         *
         * If we're in a grouping set, though, we force our requested ordering
         * to be NULLS LAST, because if we have any hope of using a sorted agg
         * for the job, we're going to be tacking on generated NULL values
         * after the corresponding groups. If the user demands nulls first,
         * another sort step is going to be inevitable, but that's the
         * planner's problem.
         */


         foreach(sl, sortClause)
         {
             SortGroupClause *sc = (SortGroupClause *) lfirst(sl);

             if (sc->tleSortGroupRef == tle->ressortgroupref)
             {
                 SortGroupClause *grpc = copyObject(sc);

                 if (!toplevel)
                 {
                     grpc->nulls_first = false;
                 }
                 *flatresult = lappend(*flatresult, grpc);
                 found = true;
                 break;
             }
         }
    }

    /*
     * If no match in ORDER BY, just add it to the result using default
     * sort/group semantics.
     */
    if (!found)
    {
        *flatresult = add_target_to_group_list(cpstate, tle, *flatresult,
                                               *targetlist, exprLocation(gexpr));
    }

    /* _something_ must have assigned us a sortgroupref by now... */

    return tle->ressortgroupref;
}

/* from PG's transformGroupClause */
static List * transform_group_clause(cypher_parsestate *cpstate,
                                     List *grouplist, List **groupingSets,
                                     List **targetlist, List *sortClause,
                                     ParseExprKind exprKind)
{
    List *result = NIL;
    List *flat_grouplist;
    List *gsets = NIL;
    ListCell *gl;
    bool hasGroupingSets = false;
    Bitmapset *seen_local = NULL;

    /*
     * Recursively flatten implicit RowExprs. (Technically this is only needed
     * for GROUP BY, per the syntax rules for grouping sets, but we do it
     * anyway.)
     */
    flat_grouplist = (List *) flatten_grouping_sets((Node *) grouplist, true,
                                                    &hasGroupingSets);

    foreach(gl, flat_grouplist)
    {
        Node       *gexpr = (Node *) lfirst(gl);

        if (IsA(gexpr, GroupingSet))
        {
            ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                            errmsg("GroupingSet is not implemented")));
            break;
        }
        else
        {
            Index ref = transform_group_clause_expr(&result, seen_local,
                                                    cpstate, gexpr, targetlist,
                                                    sortClause, exprKind, true);
            if (ref > 0)
            {
                seen_local = bms_add_member(seen_local, ref);
                if (hasGroupingSets)
                {
                    ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                            errmsg("GroupingSet is not implemented")));
                }
            }
        }
    }

    /* parser should prevent this */
    Assert(gsets == NIL || groupingSets != NULL);

    if (groupingSets)
    {
        *groupingSets = gsets;
    }

    return result;
}

static Query *transform_cypher_return(cypher_parsestate *cpstate,
                                      cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_return *self = (cypher_return *)clause->self;
    Query *query;
    List *groupClause = NIL;

    query = makeNode(Query);
    query->commandType = CMD_SELECT;

    if (clause->prev)
    {
        transform_prev_cypher_clause(cpstate, clause->prev, true);
    }

    query->targetList = transform_cypher_item_list(cpstate, self->items,
                                                   &groupClause,
                                                   EXPR_KIND_SELECT_TARGET);

    markTargetListOrigins(pstate, query->targetList);

    /* ORDER BY */
    query->sortClause = transform_cypher_order_by(cpstate, self->order_by,
                                                  &query->targetList,
                                                  EXPR_KIND_ORDER_BY);

    /* 'auto' GROUP BY (from PG's transformGroupClause) */
    query->groupClause = transform_group_clause(cpstate, groupClause,
                                                &query->groupingSets,
                                                &query->targetList,
                                                query->sortClause,
                                                EXPR_KIND_GROUP_BY);

    /* DISTINCT */
    if (self->distinct)
    {
        query->distinctClause = transformDistinctClause(
            pstate, &query->targetList, query->sortClause, false);
        query->hasDistinctOn = false;
    }
    else
    {
        query->distinctClause = NIL;
        query->hasDistinctOn = false;
    }

    /* SKIP and LIMIT */
    query->limitOffset = transform_cypher_limit(cpstate, self->skip,
                                                EXPR_KIND_OFFSET, "SKIP");
    query->limitCount = transform_cypher_limit(cpstate, self->limit,
                                               EXPR_KIND_LIMIT, "LIMIT");

    query->rtable = pstate->p_rtable;
    query->rteperminfos = pstate->p_rteperminfos;
    query->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    query->hasAggs = pstate->p_hasAggs;
    query->hasSubLinks = pstate->p_hasSubLinks;

    assign_query_collations(pstate, query);

    /* this must be done after collations, for reliable comparison of exprs */
    if (pstate->p_hasAggs ||
        query->groupClause || query->groupingSets || query->havingQual)
    {
        parse_check_aggregates(pstate, query);
    }

    return query;
}

/* see transformSortClause() */
static List *transform_cypher_order_by(cypher_parsestate *cpstate,
                                       List *sort_items, List **target_list,
                                       ParseExprKind expr_kind)
{
    ParseState *pstate = (ParseState *)cpstate;
    List *sort_list = NIL;
    ListCell *li;

    foreach (li, sort_items)
    {
        SortBy *sort_by = lfirst(li);
        TargetEntry *te;

        te = find_target_list_entry(cpstate, sort_by->node, target_list,
                                    expr_kind);

        sort_list = addTargetToSortList(pstate, te, sort_list, *target_list,
                                        sort_by);
    }

    return sort_list;
}

/* see findTargetlistEntrySQL99() */
static TargetEntry *find_target_list_entry(cypher_parsestate *cpstate,
                                           Node *node, List **target_list,
                                           ParseExprKind expr_kind)
{
    Node *expr;
    ListCell *lt;
    TargetEntry *te;

    /*
     * If the ORDER BY item is a simple identifier, check if it matches
     * an alias in the target list. This implements SQL99-compliant
     * alias matching for ORDER BY clauses.
     */
    if (IsA(node, ColumnRef))
    {
        ColumnRef *cref = (ColumnRef *)node;

        if (list_length(cref->fields) == 1)
        {
            char *name = strVal(linitial(cref->fields));

            /* Try to match an alias in the target list */
            foreach (lt, *target_list)
            {
                te = lfirst(lt);

                if (te->resname != NULL && strcmp(te->resname, name) == 0)
                {
                    return te;
                }
            }
        }
    }

    expr = transform_cypher_expr(cpstate, node, expr_kind);

    foreach (lt, *target_list)
    {
        Node *te_expr;

        te = lfirst(lt);
        te_expr = strip_implicit_coercions((Node *)te->expr);

        if (equal(expr, te_expr))
        {
            return te;
        }
    }

    te = transform_cypher_item(cpstate, node, expr, expr_kind, NULL, true);

    *target_list = lappend(*target_list, te);

    return te;
}

/* see transformLimitClause() */
static Node *transform_cypher_limit(cypher_parsestate *cpstate, Node *node,
                                    ParseExprKind expr_kind,
                                    const char *construct_name)
{
    ParseState *pstate = (ParseState *)cpstate;
    Node *qual;

    if (!node)
    {
        return NULL;
    }

    qual = transform_cypher_expr(cpstate, node, expr_kind);

    qual = coerce_to_specific_type(pstate, qual, INT8OID, construct_name);

    /* LIMIT can't refer to any variables of the current query. */
    if (contain_vars_of_level(qual, 0))
    {
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("argument of %s must not contain variables",
                        construct_name),
                 parser_errposition(pstate, locate_var_of_level(qual, 0))));
    }

    return qual;
}

static Query *transform_cypher_with(cypher_parsestate *cpstate,
                                    cypher_clause *clause)
{
    cypher_with *self = (cypher_with *)clause->self;
    cypher_return *return_clause;
    cypher_clause *wrapper;

    /* TODO: check that all items have an alias for each */

    /* WITH clause is basically RETURN clause with optional WHERE subclause */
    return_clause = make_ag_node(cypher_return);
    return_clause->distinct = self->distinct;
    return_clause->items = self->items;
    return_clause->order_by = self->order_by;
    return_clause->skip = self->skip;
    return_clause->limit = self->limit;

    wrapper = palloc(sizeof(*wrapper));
    wrapper->self = (Node *)return_clause;
    wrapper->prev = clause->prev;

    return transform_cypher_clause_with_where(cpstate, transform_cypher_return,
                                              wrapper, self->where);
}

static bool match_check_valid_label(cypher_match *match,
                                    cypher_parsestate *cpstate)
{
    ListCell *cell1;
    ListCell *cell2;
    cypher_path *path;

    foreach(cell1, match->pattern)
    {
        int i = 0;
        path = (cypher_path*) lfirst(cell1);

        foreach(cell2, path->path)
        {
            if (i % 2 == 0)
            {
                cypher_node *node = NULL;

                node = lfirst(cell2);

                if (node->label)
                {
                    label_cache_data *lcd =
                        search_label_name_graph_cache(node->label,
                                                      cpstate->graph_oid);

                    if (lcd == NULL ||
                        lcd->kind != LABEL_KIND_VERTEX)
                    {
                        return false;
                    }
                }
            }
            else
            {
                cypher_relationship *rel = NULL;

                rel = lfirst(cell2);

                if (rel->label)
                {
                    label_cache_data *lcd =
                        search_label_name_graph_cache(rel->label,
                                                      cpstate->graph_oid);

                    if (lcd == NULL || lcd->kind != LABEL_KIND_EDGE)
                    {
                        return false;
                    }
                }
            }
            i++;
        }
    }

    return true;
}

static Query *transform_cypher_clause_with_where(cypher_parsestate *cpstate,
                                                 transform_method transform,
                                                 cypher_clause *clause,
                                                 Node *where)
{
    ParseState *pstate = (ParseState *)cpstate;
    Query *query;
    Node *where_qual = NULL;

    if (where)
    {
        int rtindex;
        ParseNamespaceItem *pnsi;

        query = makeNode(Query);
        query->commandType = CMD_SELECT;

        pnsi = transform_cypher_clause_as_subquery(cpstate, transform, clause,
                                                   NULL, true);
        Assert(pnsi != NULL);
        rtindex = list_length(pstate->p_rtable);
        /* rte is the only RangeTblEntry in pstate */
        if (rtindex != 1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("invalid value for rtindex")));
        }

        /*
         * add all the target entries in pnsi to the current target list to pass
         * all the variables that are introduced in the previous clause to the
         * next clause
         */
        query->targetList = expandNSItemAttrs(pstate, pnsi, 0, true, -1);
        markTargetListOrigins(pstate, query->targetList);
        query->rtable = pstate->p_rtable;
        query->rteperminfos = pstate->p_rteperminfos;

        where_qual = transform_cypher_expr(cpstate, where, EXPR_KIND_WHERE);
        where_qual = coerce_to_boolean(pstate, where_qual, "WHERE");

        query->jointree = makeFromExpr(pstate->p_joinlist, where_qual);
        assign_query_collations(pstate, query);
    }
    else
    {
        query = transform(cpstate, clause);
    }

    query->hasSubLinks = pstate->p_hasSubLinks;
    query->hasTargetSRFs = pstate->p_hasTargetSRFs;
    query->hasAggs = pstate->p_hasAggs;

    return query;
}

static Query *transform_cypher_match(cypher_parsestate *cpstate,
                                     cypher_clause *clause)
{
    cypher_match *match_self = (cypher_match*) clause->self;
    Node *where = match_self->where;

    /*
     * Check label validity early unless the predecessor clause chain
     * contains a data-modifying operation (CREATE, SET, DELETE, MERGE).
     * DML predecessors may create new labels that are not yet in the
     * cache, so the check is deferred to after transform_prev_cypher_clause()
     * for those cases.
     */
    if (!clause_chain_has_dml(clause->prev) &&
        !match_check_valid_label(match_self, cpstate))
    {
        /* Label is invalid -- inject a false WHERE so the MATCH returns
         * zero rows. No DML predecessor here, so constant-foldable is fine. */
        match_self->where = make_false_where_clause(false);
    }

    if (has_list_comp_or_subquery((Node *)match_self->where, NULL))
    {
        match_self->where = NULL;
        return transform_cypher_clause_with_where(cpstate,
                transform_cypher_match_pattern, clause, where);
    }

    return transform_cypher_match_pattern(cpstate, clause);
}

/*
 * Function that checks if an expr has a cypher_sub_query or
 * cypher_list_comprehension.
 */
static bool has_list_comp_or_subquery(Node *expr, void *context)
{
    if (expr == NULL)
    {
        return false;
    }

    if (IsA(expr, ExtensibleNode))
    {
        if (is_ag_node(expr, cypher_sub_query) ||
            is_ag_node(expr, cypher_list_comprehension))
        {
            return true;
        }
    }

    return cypher_raw_expr_tree_walker(expr, has_list_comp_or_subquery, context);
}

/*
 * Transform the clause into a subquery. This subquery will be used
 * in a join so setup the namespace item and the created the rtr
 * for the join to use.
 */
static Node *transform_clause_for_join(cypher_parsestate *cpstate,
                                       cypher_clause *clause,
                                       RangeTblEntry **rte,
                                       ParseNamespaceItem **nsitem,
                                       Alias* alias)
{
    RangeTblRef *rtr;

    *nsitem = transform_cypher_clause_as_subquery(cpstate,
                                               transform_cypher_clause,
                                               clause, alias, false);
    *rte = (*nsitem)->p_rte;

    rtr = makeNode(RangeTblRef);
    rtr->rtindex = (*nsitem)->p_rtindex;

    return (Node *) rtr;
}

/*
 * For cases where we need to join two subqueries together (OPTIONAL MATCH and
 * MERGE) we need to take the columns available in each rte and merge them
 * together. The l_rte has precedence when there is a conflict, because that
 * means that the pattern create in the current clause is referencing a
 * variable declared in a previous clause (the l_rte). The output is the
 * res_colnames and res_colvars that are passed in.
 */
static void get_res_cols(ParseState *pstate, ParseNamespaceItem *l_pnsi,
                         ParseNamespaceItem *r_pnsi, List **res_colnames,
                         List **res_colvars)
{
    List *l_colnames, *l_colvars;
    List *r_colnames, *r_colvars;
    ListCell *r_lname, *r_lvar;
    List *colnames = NIL;
    List *colvars = NIL;

    expandRTE(l_pnsi->p_rte, l_pnsi->p_rtindex, 0, VAR_RETURNING_DEFAULT, -1, false,
              &l_colnames, &l_colvars);
    expandRTE(r_pnsi->p_rte, r_pnsi->p_rtindex, 0, VAR_RETURNING_DEFAULT, -1, false,
              &r_colnames, &r_colvars);

    /* add in all colnames and colvars from the l_rte. */
    *res_colnames = list_concat(*res_colnames, l_colnames);
    *res_colvars = list_concat(*res_colvars, l_colvars);

    /* find new columns and if they are a var, pass them in. */
    forboth(r_lname, r_colnames, r_lvar, r_colvars)
    {
        char *r_colname = strVal(lfirst(r_lname));
        ListCell *lname;
        ListCell *lvar;
        Var *var = NULL;

        forboth(lname, *res_colnames, lvar, *res_colvars)
        {
            char *colname = strVal(lfirst(lname));

            if (strcmp(r_colname, colname) == 0)
            {
                var = lfirst(lvar);
                break;
            }
        }

        if (var == NULL)
        {
            Var *v;

            /*
             * Each join (left) RTE's Var, that references a column of the
             * right RTE, needs to be marked 'nullable'.
             */
            v = lfirst(r_lvar);
            markNullableIfNeeded(pstate, v);

            colnames = lappend(colnames, lfirst(r_lname));
            colvars = lappend(colvars, v);
        }
    }

    *res_colnames = list_concat(*res_colnames, colnames);
    *res_colvars = list_concat(*res_colvars, colvars);
}

/*
 * transform_cypher_optional_match_clause
 *      Transform the previous clauses and OPTIONAL MATCH clauses to be LATERAL LEFT JOIN
 *   transform_cypher_optional_match_clause   to construct a result value.
 */
static RangeTblEntry *transform_cypher_optional_match_clause(cypher_parsestate *cpstate,
                                                             cypher_clause *clause)
{
    cypher_clause *prevclause;
    RangeTblEntry *l_rte, *r_rte;
    ParseNamespaceItem *l_nsitem, *r_nsitem;
    ParseState *pstate = (ParseState *) cpstate;
    JoinExpr* j = makeNode(JoinExpr);
    List *res_colnames = NIL, *res_colvars = NIL;
    Alias *l_alias, *r_alias;
    ParseNamespaceItem *jnsitem;
    int i = 0;

    j->jointype = JOIN_LEFT;

    l_alias = makeAlias(PREV_CYPHER_CLAUSE_ALIAS, NIL);
    r_alias = makeAlias(CYPHER_OPT_RIGHT_ALIAS, NIL);

    j->larg = transform_clause_for_join(cpstate, clause->prev, &l_rte,
                                        &l_nsitem, l_alias);
    pstate->p_namespace = lappend(pstate->p_namespace, l_nsitem);

    /*
     * Remove the previous clause so when the transform_clause_for_join function
     * transforms the OPTIONAL MATCH, the previous clause will not be transformed
     * again.
     */
    prevclause = clause->prev;
    clause->prev = NULL;

    /* set the lateral flag to true */
    pstate->p_lateral_active = true;

    j->rarg = transform_clause_for_join(cpstate, clause, &r_rte,
                                        &r_nsitem, r_alias);

    /*
     * Since this is a left join, we need to mark j->rarg as it may potentially
     * emit NULL. The jindex argument holds rtindex of the join's RTE, which is
     * created right after j->arg's RTE in this case.
     */
    markRelsAsNulledBy(pstate, j->rarg, r_nsitem->p_rtindex + 1);

    /* we are done transform the lateral left join */
    pstate->p_lateral_active = false;

    /*
     * We are done with the previous clause in the transform phase, but
     * reattach the previous clause for semantics.
     */
    clause->prev = prevclause;

    pstate->p_namespace = NIL;

    /* get the colnames and colvars from the rtes */
    get_res_cols(pstate, l_nsitem, r_nsitem, &res_colnames, &res_colvars);

    jnsitem = addRangeTableEntryForJoin(pstate,
                                        res_colnames,
                                        NULL,
                                        j->jointype,
                                        0,
                                        res_colvars,
                                        NIL,
                                        NIL,
                                        j->alias,
                                        NULL,
                                        false);

    j->rtindex = jnsitem->p_rtindex;

    for (i = list_length(pstate->p_joinexprs) + 1; i < j->rtindex; i++)
    {
        pstate->p_joinexprs = lappend(pstate->p_joinexprs, NULL);
    }
    pstate->p_joinexprs = lappend(pstate->p_joinexprs, j);
    Assert(list_length(pstate->p_joinexprs) == j->rtindex);

    pstate->p_joinlist = lappend(pstate->p_joinlist, j);

    /* add jrte to column namespace only */
    addNSItemToQuery(pstate, jnsitem, false, false, true);

    return jnsitem->p_rte;
}

static Query *transform_cypher_match_pattern(cypher_parsestate *cpstate,
                                             cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_match *self = (cypher_match *)clause->self;
    Query *query;
    Node *where = self->where;

    query = makeNode(Query);
    query->commandType = CMD_SELECT;

    if(self->optional == true && clause->next)
    {
        cypher_clause *next = clause->next;

        if (is_ag_node(next->self, cypher_match))
        {
            cypher_match *next_self = (cypher_match *)next->self;
            if (!next_self->optional)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("MATCH cannot follow OPTIONAL MATCH"),
                         parser_errposition(pstate,
                                            exprLocation((Node *) next_self))));
            }
        }
    }

    /* If there is no previous clause, transform to a general MATCH clause. */
    if (self->optional == true && clause->prev != NULL)
    {
        RangeTblEntry *rte = transform_cypher_optional_match_clause(cpstate, clause);

        query->targetList = make_target_list_from_join(pstate, rte);
        query->rtable = pstate->p_rtable;
        query->rteperminfos = pstate->p_rteperminfos;
        query->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    }
    else
    {
        if (clause->prev)
        {
            RangeTblEntry *rte;
            int rtindex;
            ParseNamespaceItem *pnsi;
            bool has_dml;

            pnsi = transform_prev_cypher_clause(cpstate, clause->prev, true);
            rte = pnsi->p_rte;

            /*
             * If the predecessor clause chain contains a data-modifying
             * operation (CREATE, SET, DELETE, MERGE), mark the subquery
             * RTE as a security barrier. This prevents PostgreSQL's
             * optimizer from pushing MATCH filter quals down into the
             * subquery, which would cause them to evaluate before the
             * DML executes -- resulting in quals checking NULL values
             * and filtering out all rows.
             */
            has_dml = clause_chain_has_dml(clause->prev);

            if (has_dml)
            {
                rte->security_barrier = true;
            }

            rtindex = list_length(pstate->p_rtable);
            /* rte is the first RangeTblEntry in pstate */
            if (rtindex != 1)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("invalid value for rtindex")));
            }

            /*
             * add all the target entries in rte to the current target list to pass
             * all the variables that are introduced in the previous clause to the
             * next clause
             */
            pnsi = get_namespace_item(pstate, rte);
            query->targetList = expandNSItemAttrs(pstate, pnsi, 0, true, -1);

            /*
             * Now that the predecessor chain is fully transformed and
             * any CREATE-generated labels exist in the cache, check
             * whether the MATCH pattern references valid labels. This
             * deferred check is only needed when the chain has DML,
             * since labels created by CREATE are not in the cache at
             * the time of the early check in transform_cypher_match().
             *
             * We use a volatile false predicate (random() IS NULL)
             * instead of a constant one (true = false) because PG's
             * planner can constant-fold the latter into a One-Time
             * Filter: false, eliminating the entire plan subtree --
             * including the DML predecessor scan -- without executing it.
             */
            if (has_dml && !match_check_valid_label(self, cpstate))
            {
                where = make_false_where_clause(true);
            }
        }

        transform_match_pattern(cpstate, query, self->pattern, where);
    }

    markTargetListOrigins(pstate, query->targetList);

    query->hasSubLinks = pstate->p_hasSubLinks;
    query->hasWindowFuncs = pstate->p_hasWindowFuncs;
    query->hasTargetSRFs = pstate->p_hasTargetSRFs;
    query->hasAggs = pstate->p_hasAggs;

    assign_query_collations(pstate, query);

    return query;
}

/*
 * Function to make a target list from an RTE. Taken from AgensGraph and PG
 */
static List *make_target_list_from_join(ParseState *pstate, RangeTblEntry *rte)
{
    List *targetlist = NIL;
    ListCell *lt;
    ListCell *ln;

    Assert(rte->rtekind == RTE_JOIN);

    forboth(lt, rte->joinaliasvars, ln, rte->eref->colnames)
    {
        Var *varnode = lfirst(lt);
        char *resname = strVal(lfirst(ln));
        TargetEntry *tmp;

        tmp = makeTargetEntry((Expr *) varnode,
                              (AttrNumber) pstate->p_next_resno++,
                              pstrdup(resname),
                              false);
        targetlist = lappend(targetlist, tmp);
    }

    return targetlist;
}

/*
 * Function to make a target list from an RTE. Borrowed from AgensGraph and PG
 */
static List *makeTargetListFromPNSItem(ParseState *pstate, ParseNamespaceItem *pnsi)
{
    List *targetlist = NIL;
    int rtindex;
    int varattno;
    ListCell *ln;
    ListCell *lt;
    RangeTblEntry *rte;
    Assert(pnsi->p_rte);
    rte = pnsi->p_rte;

    /* right now this is only for subqueries */
    Assert(rte->rtekind == RTE_SUBQUERY);

    rtindex = pnsi->p_rtindex;

    varattno = 1;
    ln = list_head(rte->eref->colnames);
    foreach(lt, rte->subquery->targetList)
    {
        TargetEntry *te = lfirst(lt);
        Var *varnode;
        char *resname;
        TargetEntry *tmp;

        if (te->resjunk)
        {
            continue;
        }

        Assert(varattno == te->resno);

        /* no transform here, just use `te->expr` */
        varnode = makeVar(rtindex, varattno, exprType((Node *) te->expr),
                          exprTypmod((Node *) te->expr),
                          exprCollation((Node *) te->expr), 0);

        resname = strVal(lfirst(ln));

        tmp = makeTargetEntry((Expr *)varnode,
                              (AttrNumber)pstate->p_next_resno++, resname,
                              false);
        targetlist = lappend(targetlist, tmp);

        varattno++;
        ln = lnext(rte->eref->colnames, ln);
    }

    return targetlist;
}

/*
 * Transform a cypher sub pattern. This is put here because it is a sub clause.
 * This works in tandem with transform_Sublink in cypher_expr.c
 */
static Query *transform_cypher_sub_pattern(cypher_parsestate *cpstate,
                                           cypher_clause *clause)
{
    cypher_match *match;
    cypher_clause *c;
    Query *qry;
    ParseState *pstate = (ParseState *)cpstate;
    cypher_sub_pattern *subpat = (cypher_sub_pattern*)clause->self;
    ParseNamespaceItem *pnsi;
    cypher_parsestate *child_parse_state = make_cypher_parsestate(cpstate);
    ParseState *p_child_parse_state = (ParseState *) child_parse_state;
    p_child_parse_state->p_expr_kind = pstate->p_expr_kind;

    /* create a cypher match node and assign it the sub pattern */
    match = make_ag_node(cypher_match);
    match->pattern = subpat->pattern;
    match->where = NULL;
    /* wrap it in a clause */
    c = palloc(sizeof(cypher_clause));
    c->self = (Node *)match;
    c->prev = NULL;
    c->next = NULL;

    /* set up a select query and run it as a sub query to the parent match */
    qry = makeNode(Query);
    qry->commandType = CMD_SELECT;

    pnsi = transform_cypher_clause_as_subquery(child_parse_state,
                                              transform_cypher_clause, c,
                                              NULL, true);

    qry->targetList = makeTargetListFromPNSItem(p_child_parse_state, pnsi);

    markTargetListOrigins(p_child_parse_state, qry->targetList);

    qry->rtable = p_child_parse_state->p_rtable;
    qry->rteperminfos = p_child_parse_state->p_rteperminfos;
    qry->jointree = makeFromExpr(p_child_parse_state->p_joinlist, NULL);

    /* the state will be destroyed so copy the data we need */
    qry->hasSubLinks = p_child_parse_state->p_hasSubLinks;
    qry->hasTargetSRFs = p_child_parse_state->p_hasTargetSRFs;
    qry->hasAggs = p_child_parse_state->p_hasAggs;

    if (qry->hasAggs)
    {
        parse_check_aggregates(p_child_parse_state, qry);
    }

    assign_query_collations(p_child_parse_state, qry);

    free_cypher_parsestate(child_parse_state);

    return qry;
}

static Query *transform_cypher_sub_query(cypher_parsestate *cpstate,
                                           cypher_clause *clause)
{
    cypher_clause *c;
    Query *qry;
    ParseState *pstate =(ParseState *)cpstate;
    cypher_sub_query *sub_query = (cypher_sub_query*)clause->self;
    ParseNamespaceItem *pnsi;
    cypher_parsestate *child_parse_state = make_cypher_parsestate(cpstate);
    ParseState *p_child_parse_state = (ParseState *) child_parse_state;
    p_child_parse_state->p_expr_kind = pstate->p_expr_kind;

    c = make_cypher_clause((List *)sub_query->query);

    qry = makeNode(Query);
    qry->commandType = CMD_SELECT;

    child_parse_state->subquery_where_flag = true;

    pnsi = transform_cypher_clause_as_subquery(child_parse_state,
                                               transform_cypher_clause,
                                               c,
                                               NULL, true);

    qry->targetList = makeTargetListFromPNSItem(p_child_parse_state, pnsi);

    markTargetListOrigins(p_child_parse_state, qry->targetList);

    qry->rtable = p_child_parse_state->p_rtable;
    qry->rteperminfos = p_child_parse_state->p_rteperminfos;
    qry->jointree = makeFromExpr(p_child_parse_state->p_joinlist, NULL);

    /* the state will be destroyed so copy the data we need */
    qry->hasSubLinks = p_child_parse_state->p_hasSubLinks;
    qry->hasTargetSRFs = p_child_parse_state->p_hasTargetSRFs;
    qry->hasAggs = p_child_parse_state->p_hasAggs;

    if (qry->hasAggs)
    {
        parse_check_aggregates(p_child_parse_state, qry);
    }

    assign_query_collations(p_child_parse_state, qry);

    free_cypher_parsestate(child_parse_state);

    return qry;
}

/*
 * Code borrowed and inspired by PG's transformFromClauseItem. This function
 * will transform the VLE function, depending on type. Currently, only
 * RangeFunctions are supported. But, others may be in the future.
 */
static Node *transform_from_clause_item(cypher_parsestate *cpstate, Node *n,
                                        RangeTblEntry **top_rte, int *top_rti,
                                        List **namespace)
{
    ParseState *pstate = &cpstate->pstate;

    /* we only care about RangeFunctions at this time */
    Assert(IsA(n, RangeFunction));

    if (IsA(n, RangeFunction))
    {
        /* function is like a plain relation */
        RangeTblRef *rtr;
        RangeTblEntry *rte;
        ParseNamespaceItem *nsitem;
        int rtindex;

        nsitem = transform_RangeFunction(cpstate, (RangeFunction *) n);
        rte = nsitem->p_rte;
        /* assume new rte is at end */
        rtindex = list_length(pstate->p_rtable);
        Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
        *top_rte = rte;
        *top_rti = rtindex;
        *namespace = list_make1(nsitem);
        rtr = makeNode(RangeTblRef);
        rtr->rtindex = rtindex;
        return (Node *) rtr;
    }

    /* if it isn't a RangeFunction, return NULL */
    return NULL;
}

/*
 * static function borrowed from PG.
 *
 * setNamespaceLateralState -
 * Convenience subroutine to update LATERAL flags in a namespace list.
 */
static void setNamespaceLateralState(List *namespace, bool lateral_only,
                                     bool lateral_ok)
{
    ListCell *lc;

    foreach(lc, namespace)
    {
        ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(lc);

        nsitem->p_lateral_only = lateral_only;
        nsitem->p_lateral_ok = lateral_ok;
    }
}

/*
 * Code borrowed and inspired by PG's transformFromClauseItem. Static function
 * to add in the VLE function as a FROM clause entry.
 */
static ParseNamespaceItem *append_VLE_Func_to_FromClause(cypher_parsestate *cpstate,
                                                         Node *n)
{
    ParseState *pstate = &cpstate->pstate;
    RangeTblEntry *rte = NULL;
    List *namespace = NULL;
    int rtindex;

    /*
     * Following PG's FROM clause logic, just in case we need to expand it in
     * the future, we process the items in another function.
     */
    n = transform_from_clause_item(cpstate, n, &rte, &rtindex, &namespace);

    /* this should not happen */
    Assert(n != NULL);

    /* verify there aren't any conflicts */
    checkNameSpaceConflicts(pstate, pstate->p_namespace, namespace);

    /* mark the new namespace items as visible only to LATERAL */
    setNamespaceLateralState(namespace, true, true);

    /* add the entry to the joinlist and namespace */
    pstate->p_joinlist = lappend(pstate->p_joinlist, n);
    pstate->p_namespace = list_concat(pstate->p_namespace, namespace);

    /* make all namespace items unconditionally visible */
    setNamespaceLateralState(pstate->p_namespace, false, true);

    return lfirst(list_head(namespace));
}

/*
 * Code borrowed from PG's transformRangeFunction
 *
 * --- transform a function call appearing in FROM
 */
static ParseNamespaceItem *transform_RangeFunction(cypher_parsestate *cpstate,
                                              RangeFunction *r)
{
    ParseState *pstate = NULL;
    List *funcexprs = NIL;
    List *funcnames = NIL;
    List *coldeflists = NIL;
    bool is_lateral = false;
    ListCell *lc = NULL;
    ParseNamespaceItem *pnsi;

    pstate = &cpstate->pstate;

    Assert(!pstate->p_lateral_active);
    pstate->p_lateral_active = true;

    /* transform the raw expressions */
    foreach(lc, r->functions)
    {
        List *pair = (List*)lfirst(lc);
        Node *fexpr;
        List *coldeflist;
        Node *newfexpr;
        Node *last_srf;

        /* Disassemble the function-call/column-def-list pairs */
        Assert(list_length(pair) == 2);
        fexpr = (Node*) linitial(pair);
        coldeflist = (List*) lsecond(pair);

        /* normal case ... */
        last_srf = pstate->p_last_srf;

        /* transform the function expression */
        newfexpr = transform_cypher_expr(cpstate, fexpr,
                                         EXPR_KIND_FROM_FUNCTION);

        /* nodeFunctionscan.c requires SRFs to be at top level */
        if (pstate->p_last_srf != last_srf &&
            pstate->p_last_srf != newfexpr)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("set-returning functions must appear at top level of FROM"),
                     parser_errposition(pstate,
                                        exprLocation(pstate->p_last_srf))));
        }

        funcexprs = lappend(funcexprs, newfexpr);
        funcnames = lappend(funcnames, FigureColname(fexpr));

        if (coldeflist && r->coldeflist)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("multiple column definition lists are not allowed for the same function"),
                     parser_errposition(pstate,
                                        exprLocation((Node *) r->coldeflist))));
        }

        coldeflists = lappend(coldeflists, coldeflist);
    }

    pstate->p_lateral_active = false;

    /*
     * We must assign collations now so that the RTE exposes correct collation
     * info for Vars created from it.
     */
    assign_list_collations(pstate, funcexprs);

    /* currently this is not used by the VLE */
    Assert(r->coldeflist == NULL);

    /* mark the RTE as LATERAL */
    is_lateral = r->lateral || contain_vars_of_level((Node *) funcexprs, 0);

    /* build an RTE for the function */
    pnsi = addRangeTableEntryForFunction(pstate, funcnames, funcexprs,
                                         coldeflists, r, is_lateral,
                                         true);

    return pnsi;
}

static void transform_match_pattern(cypher_parsestate *cpstate, Query *query,
                                    List *pattern, Node *where)
{
    ParseState *pstate = (ParseState *)cpstate;
    ListCell *lc;
    List *quals = NIL;
    Expr *q = NULL;
    Expr *expr = NULL;

    /*
     * Loop through a comma separated list of paths like (u)-[e]-(v), (w), (x)
     */
    foreach (lc, pattern)
    {
        List *qual = NULL;
        cypher_path *path = NULL;

        /* get the path and transform it */
        path = (cypher_path *) lfirst(lc);

        qual = transform_match_path(cpstate, query, path);

        quals = list_concat(quals, qual);
    }

    if (quals != NIL)
    {
        q = makeBoolExpr(AND_EXPR, quals, -1);
        expr = (Expr *)transformExpr(&cpstate->pstate, (Node *)q,
                                     EXPR_KIND_WHERE);
    }

    if (cpstate->property_constraint_quals != NIL)
    {
        Expr *prop_qual = makeBoolExpr(AND_EXPR,
                                       cpstate->property_constraint_quals, -1);

        if (expr == NULL)
        {
            expr = prop_qual;
        }
        else
        {
            expr = makeBoolExpr(AND_EXPR, list_make2(expr, prop_qual), -1);
        }
    }

    /* transform the where clause quals and add to the quals, */
    if (where != NULL)
    {
        Expr *where_qual;

        where_qual = (Expr *)transform_cypher_expr(cpstate, where,
                                                   EXPR_KIND_WHERE);
        if (expr == NULL)
        {
            expr = where_qual;
        }
        else
        {
            /*
             * coerce the WHERE clause to a boolean before AND with the property
             * constraints, otherwise there could be evaluation issues.
             */
            where_qual = (Expr *)coerce_to_boolean(pstate, (Node *)where_qual,
                                                   "WHERE");

            expr = makeBoolExpr(AND_EXPR, list_make2(expr, where_qual), -1);
        }
    }

    /*
     * Coerce to WHERE clause to a bool, denoting whether the constructed
     * clause is true or false.
     */
    if (expr != NULL)
    {
        expr = (Expr *)coerce_to_boolean(pstate, (Node *)expr, "WHERE");
    }

    query->rtable = cpstate->pstate.p_rtable;
    query->rteperminfos = cpstate->pstate.p_rteperminfos;
    query->jointree = makeFromExpr(cpstate->pstate.p_joinlist, (Node *)expr);
}

/*
 * Creates a FuncCall node that will prevent an edge from being joined
 * to twice.
 */
static FuncCall *prevent_duplicate_edges(cypher_parsestate *cpstate,
                                         List *entities)
{
    List *edges = NIL;
    ListCell *lc;
    List *qualified_function_name = NULL;
    String *ag_catalog;
    String *edge_fn = NULL;
    bool is_vle_edge = false;
    int nentities = list_length(entities);

    ag_catalog = makeString("ag_catalog");

    /* iterate through each entity, collecting the access node for each edge */
    foreach (lc, entities)
    {
        transform_entity *entity = lfirst(lc);
        Node *edge;

        if (entity->type == ENT_EDGE)
        {
            edge = make_qual(cpstate, entity, AG_EDGE_COLNAME_ID);

            edges = lappend(edges, edge);
        }
        else if (entity->type == ENT_VLE_EDGE)
        {
            is_vle_edge = true;
            edges = lappend(edges, entity->expr);
        }
    }

    if (!is_vle_edge && (nentities >= 5 && nentities <= 9))
    {
        if (nentities == 5)
        {
            edge_fn = makeString("_ag_enforce_edge_uniqueness2");
        }
        else if (nentities == 7)
        {
            edge_fn = makeString("_ag_enforce_edge_uniqueness3");
        }
        else
        {
            edge_fn = makeString("_ag_enforce_edge_uniqueness4");
        }
    }
    else
    {
        edge_fn = makeString("_ag_enforce_edge_uniqueness");
    }

    qualified_function_name = list_make2(ag_catalog, edge_fn);

    return makeFuncCall(qualified_function_name, edges, COERCE_SQL_SYNTAX, -1);
}

/*
 * For any given edge, the previous entity is joined with the edge
 * via the prev_qual node, and the next entity is join with the
 * next_qual node. If there is a filter on the previous vertex label,
 * create a filter, same with the next node.
 */
static List *make_directed_edge_join_conditions(
    cypher_parsestate *cpstate, transform_entity *prev_entity,
    transform_entity *next_entity, Node *prev_qual, Node *next_qual,
    char *prev_node_filter, char *next_node_filter)
{
    List *quals = NIL;

    if (prev_entity->in_join_tree)
    {
        quals = list_concat(quals, join_to_entity(cpstate, prev_entity,
                                                  prev_qual, JOIN_SIDE_LEFT));
    }

    if (next_entity->in_join_tree && next_entity->type != ENT_VLE_EDGE)
    {
        quals = list_concat(quals, join_to_entity(cpstate, next_entity,
                                                  next_qual, JOIN_SIDE_RIGHT));
    }

    if (prev_node_filter != NULL && !IS_DEFAULT_LABEL_VERTEX(prev_node_filter))
    {
        A_Expr *qual;
        qual = filter_vertices_on_label_id(cpstate, prev_qual,
                                           prev_node_filter);

        quals = lappend(quals, qual);
    }

    if (next_node_filter != NULL && !IS_DEFAULT_LABEL_VERTEX(next_node_filter))
    {
        A_Expr *qual;
        qual = filter_vertices_on_label_id(cpstate, next_qual,
                                           next_node_filter);

        quals = lappend(quals, qual);
    }

    return quals;
}

/*
 * The joins are driven by edges. Under specific conditions, it becomes
 * necessary to have knowledge about the previous edge and vertex and
 * the next vertex and edge.
 *
 * [prev_edge]-(prev_node)-[edge]-(next_node)-[next_edge]
 *
 * prev_edge and next_edge are allowed to be null.
 * prev_node and next_node are not allowed to be null.
 */
static List *make_join_condition_for_edge(cypher_parsestate *cpstate,
                                          transform_entity *prev_edge,
                                          transform_entity *prev_node,
                                          transform_entity *entity,
                                          transform_entity *next_node,
                                          transform_entity *next_edge)
{
    char *next_label_name_to_filter = NULL;
    char *prev_label_name_to_filter = NULL;
    transform_entity *next_entity;
    transform_entity *prev_entity;

    /*
     * When this edge is a vle edge, pass the prev and next
     * node to the match_vle_terminal_edge function to process
     * which rows match.
     */
    if (entity->type == ENT_VLE_EDGE)
    {
        Node *left_id = NULL;
        Node *right_id = NULL;
        String *ag_catalog = makeString("ag_catalog");
        String *func_name;
        List *qualified_func_name;
        List *args = NIL;
        List *quals = NIL;

        /*
         * If the next node is not in the join tree, we don't need to make any
         * quals.
         */
        if (!next_node->in_join_tree)
        {
            return NIL;
        }

        /*
         * If the previous node and the next node are in the join tree, we need
         * to create the age_match_vle_terminal_edge to compare the vle returned
         * results against the two nodes.
         */
        if (prev_node->in_join_tree)
        {
            func_name = makeString("age_match_vle_terminal_edge");
            qualified_func_name = list_make2(ag_catalog, func_name);

            /*
             * Get the vertex's id and pass to the function. Pass in NULL
             * otherwise.
             */
            left_id = (Node *)make_qual(cpstate, prev_node, "id");
            right_id = (Node *)make_qual(cpstate, next_node, "id");

            /* create the argument list */
            args = list_make3(left_id, right_id, entity->expr);

            /* add to quals */
            quals = lappend(quals, makeFuncCall(qualified_func_name, args,
                                                COERCE_EXPLICIT_CALL, -1));
        }

        /*
         * When the previous node is not in the join tree, but there is a vle
         * edge before that join, then we need to compare this vle's start node
         * against the previous vle's end node. No need to check the next edge,
         * because that would be redundant.
         */
        if (!prev_node->in_join_tree &&
            prev_edge != NULL &&
            prev_edge->type == ENT_VLE_EDGE)
        {
            List *qualified_name;
            String *match_qual;
            FuncCall *fc;

            match_qual = makeString("age_match_two_vle_edges");

            /* make the qualified function name */
            qualified_name = list_make2(ag_catalog, match_qual);

            /* make the args */
            args = list_make2(prev_edge->expr, entity->expr);

            /* create the function call */
            fc = makeFuncCall(qualified_name, args, COERCE_EXPLICIT_CALL, -1);

            quals = lappend(quals, fc);
        }

        return quals;
    }

    /*
     *  If the previous node is not in the join tree, set the previous
     *  label filter.
     */
    if (!prev_node->in_join_tree)
    {
        prev_label_name_to_filter = prev_node->entity.node->label;
    }

    /*
     * If the next node is not in the join tree and there is not
     * another edge, set the label filter. When there is another
     * edge, we don't need to set it, because that edge will set the
     * filter for that node.
     */
    if (!next_node->in_join_tree && next_edge == NULL)
    {
        next_label_name_to_filter = next_node->entity.node->label;
    }

    /*
     * When the previous node is not in the join tree, and there
     * is a previous edge, set the previous entity to that edge.
     * Otherwise, use the previous node/
     */
    if (!prev_node->in_join_tree && prev_edge != NULL)
    {
        prev_entity = prev_edge;
    }
    else
    {
        prev_entity = prev_node;
    }

    /*
     * When the next node is not in the join tree, and there
     * is a next edge, set the next entity to that edge.
     * Otherwise, use the next node.
     */
    if (!next_node->in_join_tree && next_edge != NULL)
    {
        next_entity = next_edge;
    }
    else
    {
        next_entity = next_node;
    }

    switch (entity->entity.rel->dir)
    {
        case CYPHER_REL_DIR_RIGHT:
        {
            Node *prev_qual = make_qual(cpstate, entity,
                                        AG_EDGE_COLNAME_START_ID);
            Node *next_qual = make_qual(cpstate, entity,
                                        AG_EDGE_COLNAME_END_ID);

            return make_directed_edge_join_conditions(cpstate, prev_entity,
                                                      next_node, prev_qual,
                                                      next_qual,
                                                      prev_label_name_to_filter,
                                                      next_label_name_to_filter);
        }
        case CYPHER_REL_DIR_LEFT:
        {
            Node *prev_qual = make_qual(cpstate, entity,
                                        AG_EDGE_COLNAME_END_ID);
            Node *next_qual = make_qual(cpstate, entity,
                                        AG_EDGE_COLNAME_START_ID);

            return make_directed_edge_join_conditions(cpstate, prev_entity,
                                                      next_node, prev_qual,
                                                      next_qual,
                                                      prev_label_name_to_filter,
                                                      next_label_name_to_filter);
        }
        case CYPHER_REL_DIR_NONE:
        {
            /*
             * For undirected relationships, we can use the left directed
             * relationship OR'd by the right directed relationship.
             */
            Node *start_id_expr = make_qual(cpstate, entity,
                                            AG_EDGE_COLNAME_START_ID);
            Node *end_id_expr = make_qual(cpstate, entity,
                                          AG_EDGE_COLNAME_END_ID);
            List *first_join_quals = NIL, *second_join_quals = NIL;
            Expr *first_qual, *second_qual;
            Expr *or_qual;

            first_join_quals = make_directed_edge_join_conditions(cpstate,
                                                                  prev_entity,
                                                                  next_entity,
                                                                  start_id_expr,
                                                                  end_id_expr,
                                                                  prev_label_name_to_filter,
                                                                  next_label_name_to_filter);

            second_join_quals = make_directed_edge_join_conditions(cpstate,
                                                                   prev_entity,
                                                                   next_entity,
                                                                   end_id_expr,
                                                                   start_id_expr,
                                                                   prev_label_name_to_filter,
                                                                   next_label_name_to_filter);

            first_qual = makeBoolExpr(AND_EXPR, first_join_quals, -1);
            second_qual = makeBoolExpr(AND_EXPR, second_join_quals, -1);

            or_qual = makeBoolExpr(OR_EXPR, list_make2(first_qual, second_qual),
                               -1);

            return list_make1(or_qual);
        }
        default:
            return NULL;
    }
}

/* creates a type cast node to agtype */
static Node *make_type_cast_to_agtype(Node *arg)
{
    TypeCast *n = makeNode(TypeCast);
    String *ag_catalog = makeString("ag_catalog");
    String *agtype_str = makeString("agtype");
    List *qualified_name = list_make2(ag_catalog, agtype_str);

    n->arg = arg;
    n->typeName = makeTypeNameFromNameList(qualified_name);
    n->location = -1;
    return (Node *) n;
}

/*
 * Makes an agtype bool node that Postgres' transform expression logic
 * can handle. Used when constructed the join quals for building the paths
 */
static Node *make_bool_a_const(bool state)
{
    A_Const *n = makeNode(A_Const);

    n->val.sval.type = T_String;
    n->val.sval.sval = (state ? "true" : "false");
    n->location = -1;

    /* typecast to agtype */
    return make_type_cast_to_agtype((Node *)n);
}

/*
 * For the given entity, join it to the current edge, via the passed
 * qual node. The side denotes if the entity is on the right
 * or left of the current edge. Which we will need to know if the
 * passed entity is a directed edge.
 */
static List *join_to_entity(cypher_parsestate *cpstate,
                            transform_entity *entity, Node *qual,
                            enum transform_entity_join_side side)
{
    ParseState *pstate = (ParseState *)cpstate;
    A_Expr *expr;
    List *quals = NIL;

    if (entity->type == ENT_VERTEX)
    {
        Node *id_qual = make_qual(cpstate, entity, AG_EDGE_COLNAME_ID);

        expr = makeSimpleA_Expr(AEXPR_OP, "=", qual, (Node *)id_qual, -1);

        quals = lappend(quals, expr);
    }
    else if (entity->type == ENT_EDGE)
    {
        List *edge_quals = make_edge_quals(cpstate, entity, side);

        if (list_length(edge_quals) > 1)
        {
            expr = makeSimpleA_Expr(AEXPR_IN, "=", qual,
                                    (Node *)edge_quals, -1);
        }
        else
        {
            expr = makeSimpleA_Expr(AEXPR_OP, "=", qual,
                                    linitial(edge_quals), -1);
        }

        quals = lappend(quals, expr);
    }
    else if (entity->type == ENT_VLE_EDGE)
    {
        List *qualified_name, *args;
        String *ag_catalog, *match_qual;
        bool is_left_side;
        FuncCall *fc;

        ag_catalog = makeString("ag_catalog");
        match_qual = makeString("age_match_vle_edge_to_id_qual");

        /*
         *  tells the function the location of the vle relative to the
         * edge we are joining it against.
         */
        if (side == JOIN_SIDE_LEFT)
        {
            /* [vle_edge]-()-[regular_edge] */
            is_left_side = true;
        }
        else if (side == JOIN_SIDE_RIGHT)
        {
            /* [edge]-()-[vle_edge] */
            is_left_side = false;
        }
        else
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("unknown join side found"),
                     parser_errposition(pstate, entity->entity.rel->location)));
        }

        /* make the qualified function name */
        qualified_name = list_make2(ag_catalog, match_qual);

        /* make the args */
        args = list_make3(entity->expr, qual, make_bool_a_const(is_left_side));

        /* create the function call */
        fc = makeFuncCall(qualified_name, args, COERCE_EXPLICIT_CALL, -1);

        quals = lappend(quals, fc);

    }
    else
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("unknown entity type to join to")));
    }

    return quals;
}

/* makes the quals necessary when an edge is joining to another edge. */
static List *make_edge_quals(cypher_parsestate *cpstate,
                             transform_entity *edge,
                             enum transform_entity_join_side side)
{
    ParseState *pstate = (ParseState *)cpstate;
    char *left_dir;
    char *right_dir;

    Assert(edge->type == ENT_EDGE);

    /*
     * When the rel is on the left side in a pattern, then a left directed path
     * is concerned with the start id and a right directed path is concerned
     * with the end id. When the rel is on the right side of a pattern, the
     * above statement is inverted.
     */
    switch (side)
    {
        case JOIN_SIDE_LEFT:
        {
            left_dir = AG_EDGE_COLNAME_START_ID;
            right_dir = AG_EDGE_COLNAME_END_ID;
            break;
        }
        case JOIN_SIDE_RIGHT:
        {
            left_dir = AG_EDGE_COLNAME_END_ID;
            right_dir = AG_EDGE_COLNAME_START_ID;
            break;
        }
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("unknown join type found"),
                     parser_errposition(pstate, edge->entity.rel->location)));
    }

    switch (edge->entity.rel->dir)
    {
        case CYPHER_REL_DIR_LEFT:
        {
            return list_make1(make_qual(cpstate, edge, left_dir));
        }
        case CYPHER_REL_DIR_RIGHT:
        {
            return list_make1(make_qual(cpstate, edge, right_dir));
        }
        case CYPHER_REL_DIR_NONE:
        {
            return list_make2(make_qual(cpstate, edge, left_dir),
                              make_qual(cpstate, edge, right_dir));
        }
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("Unknown relationship direction")));
    }
    return NIL;
}

/*
 * Creates a node that will create a filter on the passed field node
 * that removes all labels that do not have the same label_id
 */
static A_Expr *filter_vertices_on_label_id(cypher_parsestate *cpstate,
                                           Node *id_field, char *label)
{
    label_cache_data *lcd = search_label_name_graph_cache(label,
                                                          cpstate->graph_oid);
    A_Const *n;
    FuncCall *fc;
    String *ag_catalog, *extract_label_id;
    int32 label_id = lcd->id;

    n = makeNode(A_Const);
    n->val.ival.type = T_Integer;
    n->val.ival.ival = label_id;
    n->location = -1;

    ag_catalog = makeString("ag_catalog");
    extract_label_id = makeString("_extract_label_id");

    fc = makeFuncCall(list_make2(ag_catalog, extract_label_id),
                      list_make1(id_field), COERCE_EXPLICIT_CALL, -1);

    return makeSimpleA_Expr(AEXPR_OP, "=", (Node *)fc, (Node *)n, -1);
}

/*
 * Makes property constraint using indirection(s). This is an
 * alternative to using the containment operator (@>).
 * 
 * Consider the following query
 * 
 *      MATCH (x:Label{
 *        name: 'xyz',
 *        address: {
 *          city: 'abc',
 *          street: {
 *              name: 'pqr',
 *              number: 123
 *          }
 *        },
 *        phone: [9, 8, 7],
 *        parents: {}
 *      })
 *
 * There are two cases:
 * 
 * 1- When use_equals flag is set, the above query is tranformed to-
 * 
 *     x.name = 'xyz' AND
 *     x.address = {"city": "abc", "street": {"name": "pqr", "number": 123}} AND
 *     x.phone = [9, 8, 7] AND
 *     x.parents = {}
 * 
 * 2- When use_equals flag is not set, the above query is tranformed to-
 *
 *      x.name = 'xyz' AND
 *      x.address.city = 'abc' AND
 *      x.address.street.name = 'pqr' AND
 *      x.address.street.number = 123 AND
 *      x.phone @> [6, 4, 3] AND
 *      x.parents @> {}
 * 
 * NOTE: In case of array and empty map, containment is used instead of equality.
 */
static Node *transform_map_to_ind(cypher_parsestate *cpstate,
                                  transform_entity *entity, cypher_map *map)
{
    List *quals; /* list of equality and/or containment qual node */

    if (entity->entity.node->use_equals)
    {
        /* Case 1 */
        quals = transform_map_to_ind_top_level(cpstate, entity, map);
    }
    else
    {
        /* Case 2 */
        quals = transform_map_to_ind_recursive(cpstate, entity, map, NIL);
    }

    Assert(quals != NIL);

    if (list_length(quals) > 1)
    {
        return (Node *)makeBoolExpr(AND_EXPR, quals, -1);
    }
    else
    {
        return (Node *)linitial(quals);
    }
}

/*
 * Helper function of `transform_map_to_ind`.
 *
 * This function is called when a value of the `map` is a non-empty map.
 * For example, the key `address.street` has a non-empty map. The
 * `parent_fields` parameter will be set to the list of parents of the
 * key `street` in order. In this case, only `address`. If no parent
 * fields, set it to NIL.
 */
static List *transform_map_to_ind_recursive(cypher_parsestate *cpstate,
                                            transform_entity *entity,
                                            cypher_map *map,
                                            List *parent_fields)
{
    int i;
    ParseState *pstate;
    Node *last_srf;
    List *quals;

    pstate = (ParseState *)cpstate;
    last_srf = pstate->p_last_srf;
    quals = NIL;

    /* since this function recurses, it could be driven to stack overflow */
    check_stack_depth();

    Assert(list_length(map->keyvals) != 0);

    for (i = 0; i < map->keyvals->length; i += 2)
    {
        Node *key;
        Node *val;
        char *keystr;

        key = (Node *)map->keyvals->elements[i].ptr_value;
        val = (Node *)map->keyvals->elements[i + 1].ptr_value;
        Assert(IsA(key, String));
        keystr = ((String *)key)->sval;

        if (is_ag_node(val, cypher_map) &&
            list_length(((cypher_map *)val)->keyvals) != 0)
        {
            List *new_parent_fields;
            List *recursive_quals;

            new_parent_fields = lappend(list_copy(parent_fields),
                                        makeString(keystr));

            recursive_quals = transform_map_to_ind_recursive(
                cpstate, entity, (cypher_map *)val, new_parent_fields);

            quals = list_concat(quals, recursive_quals);

            list_free(new_parent_fields);
            list_free(recursive_quals);
        }
        else
        {
            Node *qual;
            Node *lhs;
            Node *rhs;
            List *op;
            A_Indirection *indir;
            ColumnRef *variable;

            /*
             * Lists and empty maps are transformed to containment. If a map
             * makes it here, then it must be empty. Because non-empty maps
             * are processed in the upper if-block.
             */
            if (is_ag_node(val, cypher_list) || is_ag_node(val, cypher_map))
            {
                op = list_make1(makeString("@>"));
            }
            else
            {
                op = list_make1(makeString("="));
            }

            variable = makeNode(ColumnRef);
            variable->fields =
                list_make1(makeString(entity->entity.node->name));
            variable->location = -1;

            indir = makeNode(A_Indirection);
            indir->arg = (Node *)variable;
            indir->indirection = lappend(list_copy(parent_fields),
                                         makeString(keystr));

            lhs = transform_cypher_expr(cpstate, (Node *)indir,
                                        EXPR_KIND_WHERE);
            rhs = transform_cypher_expr(cpstate, val, EXPR_KIND_WHERE);

            qual = (Node *)make_op(pstate, op, lhs, rhs, last_srf, -1);
            quals = lappend(quals, qual);
        }
    }

    return quals;
}

/*
 * Helper function of `transform_map_to_ind`.
 *
 * Transforms the map to a list of equality irrespective of
 * value type. For example,
 *
 * x.name = 'xyz'
 * x.map = {"city": "abc", "street": {"name": "pqr", "number": 123}}
 * x.list = [9, 8, 7]
 */
static List *transform_map_to_ind_top_level(cypher_parsestate *cpstate,
                                            transform_entity *entity,
                                            cypher_map *map)
{
    int i;
    ParseState *pstate;
    Node *last_srf;
    List *quals;

    pstate = (ParseState *)cpstate;
    last_srf = pstate->p_last_srf;
    quals = NIL;

    Assert(list_length(map->keyvals) != 0);

    for (i = 0; i < map->keyvals->length; i += 2)
    {
        Node *key;
        Node *val;
        Node *qual;
        Node *lhs;
        Node *rhs;
        List *op;
        A_Indirection *indir;
        ColumnRef *variable;
        char *keystr;

        key = (Node *)map->keyvals->elements[i].ptr_value;
        val = (Node *)map->keyvals->elements[i + 1].ptr_value;
        Assert(IsA(key, String));
        keystr = ((String *)key)->sval;

        op = list_make1(makeString("="));
        variable = makeNode(ColumnRef);
        variable->fields =
            list_make1(makeString(entity->entity.node->name));
        variable->location = -1;

        indir = makeNode(A_Indirection);
        indir->arg = (Node *)variable;
        indir->indirection = list_make1(makeString(keystr));

        lhs = transform_cypher_expr(cpstate, (Node *)indir,
                                    EXPR_KIND_WHERE);
        rhs = transform_cypher_expr(cpstate, val, EXPR_KIND_WHERE);

        qual = (Node *)make_op(pstate, op, lhs, rhs, last_srf, -1);
        quals = lappend(quals, qual);
    }

    return quals;
}

/*
 * Creates the property constraints for a vertex/edge in a MATCH clause.
 */
static Node *create_property_constraints(cypher_parsestate *cpstate,
                                         transform_entity *entity,
                                         Node *property_constraints,
                                         Node *prop_expr)
{
    ParseState *pstate = (ParseState *)cpstate;
    char *entity_name;
    Node *const_expr;
    Node *last_srf = pstate->p_last_srf;
    ParseNamespaceItem *pnsi;

    Assert(entity->type != ENT_PATH);

    /*
     * If the prop_expr node wasn't passed in, create it. Otherwise, skip
     * the creation step.
     */
    if (prop_expr == NULL)
    {
        ColumnRef *cr = NULL;

        cr = makeNode(ColumnRef);
        entity_name = get_entity_name(entity);
        cr->fields = list_make2(makeString(entity_name),
                                makeString("properties"));

        /* use Postgres to get the properties' transform node */
        pnsi = find_pnsi(cpstate, entity_name);
        if (pnsi != NULL)
        {
            prop_expr = scanNSItemForColumn(pstate, pnsi, 0,
                                            AG_VERTEX_COLNAME_PROPERTIES, -1);
        }
        else
        {
            prop_expr = transformExpr(pstate, (Node *)cr, EXPR_KIND_WHERE);
        }
    }

    /* use cypher to get the constraints' transform node */
    const_expr = transform_cypher_expr(cpstate, property_constraints,
                                       EXPR_KIND_WHERE);

    if (age_enable_containment)
    {
        if ((entity->type == ENT_VERTEX && entity->entity.node->use_equals) ||
            ((entity->type == ENT_EDGE || entity->type == ENT_VLE_EDGE) &&
             entity->entity.rel->use_equals))
        {
            return (Node *)make_op(pstate, list_make1(makeString("@>>")),
                                   prop_expr, const_expr, last_srf, -1);
        }
        else
        {
            return (Node *)make_op(pstate, list_make1(makeString("@>")),
                                   prop_expr, const_expr, last_srf, -1);
        }
    }
    else
    {
        return (Node *)transform_map_to_ind(
            cpstate, entity, (cypher_map *)property_constraints);
    }
}

/*
 * For the given path, transform each entity within the path, create
 * the path variable if needed, and construct the quals to enforce the
 * correct join tree, and enforce edge uniqueness.
 */
static List *transform_match_path(cypher_parsestate *cpstate, Query *query,
                                  cypher_path *path)
{
    ParseState *pstate = (ParseState *)cpstate;
    List *qual = NIL;
    List *entities = NIL;
    FuncCall *duplicate_edge_qual;
    List *join_quals;

    /* transform the entities in the path */
    entities = transform_match_entities(cpstate, query, path);

    /* create the path variable, if needed. */
    if (path->var_name != NULL)
    {
        TargetEntry *path_te;

        if (findTarget(query->targetList, path->var_name) != NULL)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_ALIAS),
                    errmsg("variable \"%s\" already exists",
                            path->var_name),
                    parser_errposition(pstate, path->location)));
        }

        path_te = transform_match_create_path_variable(cpstate, path,
                                                       entities);
        query->targetList = lappend(query->targetList, path_te);
    }

    /* construct the quals for the join tree */
    join_quals = make_path_join_quals(cpstate, entities);
    qual = list_concat(qual, join_quals);

    /* construct the qual to prevent duplicate edges */
    if (list_length(entities) > 3)
    {
        duplicate_edge_qual = prevent_duplicate_edges(cpstate, entities);
        qual = lappend(qual, duplicate_edge_qual);
    }

    return qual;
}

static transform_entity *transform_VLE_edge_entity(cypher_parsestate *cpstate,
                                                   cypher_relationship *rel,
                                                   Query *query)
{
    ParseState *pstate = NULL;
    TargetEntry *te = NULL;
    RangeFunction *rf = NULL;
    FuncCall *func = NULL;
    Alias *alias = NULL;
    Node *var = NULL;
    transform_entity *vle_entity = NULL;
    ParseNamespaceItem *pnsi;

    /* it better be a function call node */
    Assert(IsA(rel->varlen, FuncCall));

    /* get the function */
    func = (FuncCall*)rel->varlen;

    /* only our functions are supported here */
    if (list_length(func->funcname) != 1)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("only AGE functions are supported here")));
    }

    /* set the pstate */
    pstate = &cpstate->pstate;

    /* make a RangeFunction node */
    rf = makeNode(RangeFunction);
    rf->lateral = false;
    rf->ordinality = false;
    rf->is_rowsfrom = false;
    rf->functions = list_make1(list_make2(rel->varlen, NIL));

    /*
     * Build an alias for the RangeFunction. This is needed so we
     * can chain VLEs together
     */
    alias = makeNode(Alias);
    alias->aliasname = get_next_default_alias(cpstate);
    alias->colnames = NIL;
    rf->alias = alias;

    /*
     * Add the RangeFunction to the FROM clause
     */
    pnsi = append_VLE_Func_to_FromClause(cpstate, (Node*)rf);
    Assert(pnsi != NULL);

    /* Get the var node for the VLE functions column name. */
    var = scanNSItemForColumn(pstate, pnsi, 0, "edges", -1);
    Assert(var != NULL);

    /*
     * If we have a variable name (rel name), make the target entry. Otherwise,
     * there isn't a reason to create one. Additionally, verify that it is not
     * reused.
     */
    if (rel->name != NULL)
    {
        FuncExpr *fexpr;
        List *args = list_make1(var);
        Oid func_oid = InvalidOid;
        transform_entity *entity = NULL;

        te = findTarget(query->targetList, rel->name);
        entity = find_variable(cpstate, rel->name);

        /* If the variable already exists, error out */
        if (te && entity)
        {
            if (entity->type == ENT_VERTEX)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for a vertex", rel->name),
                        parser_errposition(pstate, rel->location)));
            }
            else if (entity->type == ENT_EDGE)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for an edge", rel->name),
                        parser_errposition(pstate, rel->location)));
            }
            else if (entity->type == ENT_PATH)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for a path", rel->name),
                        parser_errposition(pstate, rel->location)));
            }
            else
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("duplicate variable '%s'", rel->name),
                        parser_errposition(pstate, rel->location)));
            }
        }
        else if (te && !entity)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_ALIAS),
                     errmsg("variable '%s' already exists", rel->name),
                     parser_errposition(pstate, rel->location)));
        }

        /*
         * Get the oid for the materialize function that returns a list of
         * edges. For a VLE edge variable we need to return a list of edges,
         * not a path.
         */
        func_oid = get_ag_func_oid("age_materialize_vle_edges", 1, AGTYPEOID);

        /* build the expr node for the function */
        fexpr = makeFuncExpr(func_oid, AGTYPEOID, args, InvalidOid, InvalidOid,
                             COERCE_EXPLICIT_CALL);

        /* make the target entry and apply the provided variable */
        te = makeTargetEntry((Expr*)fexpr, pstate->p_next_resno++, rel->name,
                             false);
        /* add it to the query */
        query->targetList = lappend(query->targetList, te);
    }

    /* Make a transform entity for the vle. */
    vle_entity = make_transform_entity(cpstate, ENT_VLE_EDGE, (Node *)rel,
                                       (Expr *)var);

    /* return the vle entity */
    return vle_entity;
}

/* helper function to check for specific VLE cases */
static bool isa_special_VLE_case(cypher_path *path)
{
    cypher_relationship *cr = NULL;

    if (path->var_name == NULL)
    {
        return false;
    }

    if (list_length(path->path) != 3)
    {
        return false;
    }

    cr = (cypher_relationship*)lfirst(lnext(path->path, list_head(path->path)));

    if (cr->varlen != NULL)
    {
        return true;
    }

    return false;
}

static bool path_check_valid_label(cypher_path *path,
                                   cypher_parsestate *cpstate)
{
    ListCell *lc = NULL;
    int i = 0;

    foreach (lc, path->path)
    {
        if (i % 2 == 0)
        {
            cypher_node *node = NULL;

            node = lfirst(lc);

            if (node->label)
            {
                label_cache_data *lcd =
                    search_label_name_graph_cache(node->label,
                                                  cpstate->graph_oid);

                if (lcd == NULL || lcd->kind != LABEL_KIND_VERTEX)
                {
                    return false;
                }
            }
        }
        else
        {
            cypher_relationship *rel = NULL;

            rel = lfirst(lc);

            if (rel->label)
            {
                label_cache_data *lcd =
                    search_label_name_graph_cache(rel->label,
                                                  cpstate->graph_oid);

                if (lcd == NULL || lcd->kind != LABEL_KIND_EDGE)
                {
                    return false;
                }
            }
        }
        i++;
    }

    return true;
}

/*
 * Iterate through the path and construct all edges and necessary vertices
 */
static List *transform_match_entities(cypher_parsestate *cpstate, Query *query,
                                      cypher_path *path)
{
    ParseState *pstate = (ParseState *)cpstate;
    ListCell *lc = NULL;
    List *entities = NIL;
    int i = 0;
    bool node_declared_in_prev_clause = false;
    transform_entity *prev_entity = NULL;
    bool special_VLE_case = false;
    bool valid_label = true;

    special_VLE_case = isa_special_VLE_case(path);
    valid_label = path_check_valid_label(path, cpstate);

    /*
     * Iterate through every node in the path, construct the expr node
     * that is needed for the remaining steps
     */

    foreach (lc, path->path)
    {
        Expr *expr = NULL;
        transform_entity *entity = NULL;


        /* even increments of i are vertices */
        if (i % 2 == 0)
        {
            cypher_node *node = NULL;
            bool output_node = false;

            node = lfirst(lc);

            /*
             * The vle needs to know if the start vertex was
             * created in a previous clause. Check to see if it
             * was so the edge logic can handle changing its argument
             * if necessary.
             */
            if (node->name != NULL)
            {
                Node *expr;

                if (path->var_name && strcmp(node->name, path->var_name) == 0)
                {
                    ereport(ERROR,
                           (errcode(ERRCODE_DUPLICATE_ALIAS),
                            errmsg("variable \"%s\" is for a path",
                                    node->name),
                            parser_errposition(pstate, node->location)));
                }

                /*
                 * Checks the previous clauses to see if the variable already
                 * exists.
                 */
                expr = colNameToVar(pstate, node->name, false,
                                          node->location);
                if (expr != NULL)
                {
                    node_declared_in_prev_clause = true;
                }
            }

            /* should we make the node available */
            output_node = (special_VLE_case && !node->name && !node->props) ?
                          false :
                          INCLUDE_NODE_IN_JOIN_TREE(path, node);
            /*
             * TODO
             *
             * We need to re-evaluate if we want to use output_node or not.
             * If output_node is set to false, then it basically short circuits
             * the match for instances where a variable isn't specified. While,
             * on the surface, this appears to be a good way to improve
             * execution time of commands that won't do anything, it also
             * causes chained commands to not work correctly. This is because
             * a match without a variable will still feed its tuples to the next
             * stage(s). With this set to false, it won't. So we likely need to
             * remove all of the output_node logic. This needs to be reviewed,
             * though. For now, we just set it to true and update the output of
             * the regression tests.
             */
            output_node = true;

            /* transform vertex */
            expr = transform_cypher_node(cpstate, node, &query->targetList,
                                         output_node, valid_label);

            entity = make_transform_entity(cpstate, ENT_VERTEX, (Node *)node,
                                           expr);

            /*
             * We want to add transformed entity to entities before transforming props
             * so that props referencing currently transformed entity can be resolved.
             */
            cpstate->entities = lappend(cpstate->entities, entity);
            entities = lappend(entities, entity);

            /* transform the properties if they exist */
            if (node->props)
            {
                Node *n = NULL;
                Node *prop_var = NULL;
                Node *prop_expr = NULL;

                /*
                 * We need to build a transformed properties(prop_var)
                 * expression IF the properties variable already exists from a
                 * previous clause. Please note that the "found" prop_var was
                 * previously transformed.
                 */

                /* get the prop_var if it was previously resolved */
                if (node->name != NULL)
                {
                    prop_var = colNameToVar(pstate, node->name, false,
                                            node->location);
                }

                /*
                 * If prop_var exists and is an alias, just pass it through by
                 * assigning the prop_expr the prop_var.
                 */
                if (prop_var != NULL &&
                    pg_strncasecmp(node->name, AGE_DEFAULT_ALIAS_PREFIX,
                                   strlen(AGE_DEFAULT_ALIAS_PREFIX)) == 0)
                {
                    prop_expr = prop_var;
                }
                /*
                 * Else, if it exists and is not an alias, create the prop_expr
                 * as a transformed properties(prop_var) function node.
                 */
                else if (prop_var != NULL)
                {
                    /*
                     * Remember that prop_var is already transformed. We need
                     * to built the transform manually.
                     */
                    FuncCall *fc = NULL;
                    List *targs = NIL;
                    List *fname = NIL;

                    targs = lappend(targs, prop_var);
                    fname = list_make2(makeString("ag_catalog"),
                                       makeString("age_properties"));
                    fc = makeFuncCall(fname, targs, COERCE_SQL_SYNTAX, -1);

                    /*
                     * Hand off to ParseFuncOrColumn to create the function
                     * expression for properties(prop_var)
                     */
                    prop_expr = ParseFuncOrColumn(pstate, fname, targs,
                                                  pstate->p_last_srf, fc, false,
                                                  -1);
                }

                ((cypher_map*)node->props)->keep_null = true;
                n = create_property_constraints(cpstate, entity, node->props,
                                                prop_expr);

                cpstate->property_constraint_quals =
                    lappend(cpstate->property_constraint_quals, n);
            }

            prev_entity = entity;
        }
        /* odd increments of i are edges */
        else
        {
            cypher_relationship *rel = NULL;

            rel = lfirst(lc);

            if (rel->name && path->var_name &&
                strcmp(rel->name, path->var_name) == 0)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable \"%s\" is for a path",
                                rel->name),
                        parser_errposition(pstate, rel->location)));
            }

            /*
             * There are 2 edge cases - 1) a regular edge and 2) a VLE edge.
             * A VLE edge is not added like a regular edge - it is a function.
             */

            /* if it is a regular edge */
            if (rel->varlen == NULL)
            {
                /*
                 * In the case where the MATCH is one edge and two vertices, the
                 * edge is bidirectional, and neither vertex is included in the
                 * join tree, we need to force one of the vertices into the join
                 * tree to ensure the output is generated correctly.
                 */
                if (list_length(path->path) == 3 &&
                        rel->dir == CYPHER_REL_DIR_NONE &&
                        !prev_entity->in_join_tree)
                {
                    cypher_node *node = (cypher_node *)lfirst(lnext(path->path, lc));

                    if (!INCLUDE_NODE_IN_JOIN_TREE(path, node))
                    {
                        /*
                         * Assigning a variable name here will ensure that when
                         * the next vertex is processed, the vertex will be
                         * included in the join tree.
                         */
                        node->name = get_next_default_alias(cpstate);
                    }
                }

                expr = transform_cypher_edge(cpstate, rel, &query->targetList,
                                             valid_label);

                entity = make_transform_entity(cpstate, ENT_EDGE, (Node *)rel,
                                               expr);

                /*
                 * We want to add transformed entity to entities before transforming props
                 * so that props referencing currently transformed entity can be resolved.
                 */
                cpstate->entities = lappend(cpstate->entities, entity);
                entities = lappend(entities, entity);

                if (rel->props)
                {
                    Node *r = NULL;
                    Node *prop_var = NULL;
                    Node *prop_expr = NULL;

                    /*
                     * We need to build a transformed properties(prop_var)
                     * expression IF the properties variable already exists from
                     * a previous clause. Please note that the "found" prop_var
                     * was previously transformed.
                     */

                    /* get the prop_var if it was previously resolved */
                    if (rel->name != NULL)
                    {
                        prop_var = colNameToVar(pstate, rel->name, false,
                                                rel->location);
                    }

                    /*
                     * If prop_var exists and is an alias, just pass it through by
                     * assigning the prop_expr the prop_var.
                     */
                    if (prop_var != NULL &&
                        pg_strncasecmp(rel->name, AGE_DEFAULT_ALIAS_PREFIX,
                                       strlen(AGE_DEFAULT_ALIAS_PREFIX)) == 0)
                    {
                        prop_expr = prop_var;
                    }
                    /*
                     * Else, if it exists and is not an alias, create the prop_expr
                     * as a transformed properties(prop_var) function node.
                     */
                    else if (prop_var != NULL)
                    {
                        /*
                         * Remember that prop_var is already transformed. We need
                         * to built the transform manually.
                         */
                        FuncCall *fc = NULL;
                        List *targs = NIL;
                        List *fname = NIL;

                        targs = lappend(targs, prop_var);
                        fname = list_make2(makeString("ag_catalog"),
                                           makeString("age_properties"));
                        fc = makeFuncCall(fname, targs, COERCE_SQL_SYNTAX, -1);

                        /*
                         * Hand off to ParseFuncOrColumn to create the function
                         * expression for properties(prop_var)
                         */
                        prop_expr = ParseFuncOrColumn(pstate, fname, targs,
                                                      pstate->p_last_srf, fc,
                                                      false, -1);
                    }

                    ((cypher_map*)rel->props)->keep_null = true;
                    r = create_property_constraints(cpstate, entity, rel->props,
                                                    prop_expr);

                    cpstate->property_constraint_quals =
                        lappend(cpstate->property_constraint_quals, r);
                }

                prev_entity = entity;
            }
            /* if we have a VLE edge */
            else
            {
                transform_entity *vle_entity = NULL;

                /*
                 * Check to see if the previous node was originally created
                 * in a preceding clause. If it was, then remove the id field
                 * from the column ref. Just reference the agtype vertex
                 * variable that the prev clause created and the vle will handle
                 * extracting the id.
                 */
                if (node_declared_in_prev_clause)
                {
                    FuncCall *func = (FuncCall*)rel->varlen;

                    ColumnRef *cr = linitial(func->args);

                    Assert(IsA(cr, ColumnRef));
                    Assert(list_length(cr->fields) == 2);

                    cr->fields = list_make1(linitial(cr->fields));
                }

                /* make a transform entity for the vle */
                vle_entity = transform_VLE_edge_entity(cpstate, rel, query);

                /* add the entity in */
                cpstate->entities = lappend(cpstate->entities, vle_entity);
                entities = lappend(entities, vle_entity);

                prev_entity = entity;
            }

            node_declared_in_prev_clause = false;
        }

        i++;
    }
    return entities;
}

/*
 * Iterate through the list of entities setup the join conditions. Joins
 * are driven through edges. To correctly setup the joins, we must
 * acquire information about the previous edge and vertex, and the next
 * edge and vertex.
 */
static List *make_path_join_quals(cypher_parsestate *cpstate, List *entities)
{
    transform_entity *prev_node = NULL, *prev_edge = NULL, *edge = NULL,
                     *next_node = NULL, *next_edge = NULL;
    ListCell *lc;
    List *quals = NIL;
    List *join_quals;

    /* for vertex only queries, there is no work to do */
    if (list_length(entities) < 3)
    {
        return NIL;
    }

    lc = list_head(entities);
    for (;;)
    {
        /*
         * Initial setup, set the initial vertex as the previous vertex
         * and get the first edge
         */
        if (prev_node == NULL)
        {
            prev_node = lfirst(lc);
            lc = lnext(entities, lc);
            edge = lfirst(lc);
        }

        /* Retrieve the next node and edge in the pattern. */
        if (lnext(entities, lc) != NULL)
        {
            lc = lnext(entities, lc);
            next_node = lfirst(lc);

            if (lnext(entities, lc) != NULL)
            {
                lc = lnext(entities, lc);
                next_edge = lfirst(lc);
            }
        }

        /* create the join quals for the node */
        join_quals = make_join_condition_for_edge(cpstate, prev_edge, prev_node,
                                                  edge, next_node, next_edge);

        quals = list_concat(quals, join_quals);

        /* Set the edge as the previous edge and the next edge as
         * the current edge. If there is not a new edge, exit the
         * for loop.
         */
        prev_edge = edge;
        prev_node = next_node;
        edge = next_edge;
        next_node = NULL;
        next_edge = NULL;

        if (edge == NULL)
        {
            return quals;
        }
    }
}

/*
 * Create the path variable. Takes the list of entities, extracts the variable
 * and passes as the argument list for the _agtype_build_path function.
 */
static TargetEntry *
transform_match_create_path_variable(cypher_parsestate *cpstate,
                                     cypher_path *path, List *entities)
{
    ParseState *pstate = (ParseState *)cpstate;
    Oid build_path_oid = InvalidOid;
    Expr *expr = NULL;
    int resno = -1;
    List *entity_exprs = NIL;
    ListCell *lc = NULL;
    bool null_path_entity = false;

    if (list_length(entities) < 1)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("paths require at least 1 vertex"),
                 parser_errposition(pstate, path->location)));
    }

    /* extract the expr for each entity */
    foreach (lc, entities)
    {
        transform_entity *entity = lfirst(lc);

        if (entity->expr != NULL)
        {
            /*
             * Is it a NULL constant, meaning there was an invalid label?
             * If so, flag it for later
             */
            if (IsA(entity->expr, Const) &&
                ((Const*)(entity->expr))->constisnull)
            {
                null_path_entity = true;
            }

            entity_exprs = lappend(entity_exprs, entity->expr);
        }
    }

    /* get the oid for the path creation function */
    build_path_oid = get_ag_func_oid("_agtype_build_path", 1, ANYOID);

    /*
     * If we have a NULL in the path, there is an invalid label, so there aren't
     * any paths to be selected - the path variable will be NULL. In this case
     * we need to return a NULL constant instead.
     */
    if (null_path_entity)
    {
        expr = (Expr*)makeNullConst(AGTYPEOID, -1, InvalidOid);
    }
    /* otherwise, build the expr node for the function */
    else
    {
        transform_entity *entity;
        expr = (Expr*)makeFuncExpr(build_path_oid, AGTYPEOID, entity_exprs,
                                   InvalidOid, InvalidOid,
                                   COERCE_EXPLICIT_CALL);

        entity = make_transform_entity(cpstate, ENT_PATH, (Node *)path, expr);
        cpstate->entities = lappend(cpstate->entities, entity);
    }

    resno = cpstate->pstate.p_next_resno++;

    /* create the target entry */
    return makeTargetEntry(expr, resno, path->var_name, false);
}

/*
 * Maps a column name to the a function access name. In others word when
 * passed the name for the vertex's id column name, return the function name
 * for the vertex's agtype id element, etc.
 */
static char *get_accessor_function_name(enum transform_entity_type type,
                                        char *name)
{
    if (type == ENT_VERTEX)
    {
        /* id */
        if (!strcmp(AG_VERTEX_COLNAME_ID, name))
        {
            return AG_VERTEX_ACCESS_FUNCTION_ID;
        }
        /* props */
        else if (!strcmp(AG_VERTEX_COLNAME_PROPERTIES, name))
        {
            return AG_VERTEX_ACCESS_FUNCTION_PROPERTIES;
        }
    }
    if (type == ENT_EDGE)
    {
        /* id */
        if (!strcmp(AG_EDGE_COLNAME_ID, name))
        {
            return AG_EDGE_ACCESS_FUNCTION_ID;
        }
        /* start id */
        else if (!strcmp(AG_EDGE_COLNAME_START_ID, name))
        {
            return AG_EDGE_ACCESS_FUNCTION_START_ID;
        }
        /* end id */
        else if (!strcmp(AG_EDGE_COLNAME_END_ID, name))
        {
            return AG_EDGE_ACCESS_FUNCTION_END_ID;
        }
        /* props */
        else if (!strcmp(AG_VERTEX_COLNAME_PROPERTIES, name))
        {
            return AG_VERTEX_ACCESS_FUNCTION_PROPERTIES;
        }
    }

    ereport(ERROR,
            (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
             errmsg("column %s does not have an accessor function", name)));

    /* keeps compiler silent */
    return NULL;
}

/*
 * For the given entity and column name, construct an expression that will
 * access the column or get the access function if the entity is a variable.
 */
static Node *make_qual(cypher_parsestate *cpstate,
                       transform_entity *entity, char *col_name)
{
    List *qualified_name, *args;
    Node *node;

    if (IsA(entity->expr, Var))
    {
        char *function_name;

        function_name = get_accessor_function_name(entity->type, col_name);

        qualified_name = list_make2(makeString("ag_catalog"),
                                    makeString(function_name));


        args = list_make1(entity->expr);
        node = (Node *)makeFuncCall(qualified_name, args, COERCE_EXPLICIT_CALL,
                                    -1);
    }
    else
    {
        char *entity_name;
        ColumnRef *cr = makeNode(ColumnRef);

        if (entity->type == ENT_EDGE)
        {
            entity_name = entity->entity.node->name;
        }
        else if (entity->type == ENT_VERTEX)
        {
            entity_name = entity->entity.rel->name;
        }
        else
        {
            ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                            errmsg("unknown entity type")));
        }

        cr->fields = list_make2(makeString(entity_name), makeString(col_name));

        node = (Node *)cr;
    }

    return node;
}

static Expr *transform_cypher_edge(cypher_parsestate *cpstate,
                                   cypher_relationship *rel,
                                   List **target_list,
                                   bool valid_label)
{
    ParseState *pstate = (ParseState *)cpstate;
    char *schema_name = NULL;
    char *rel_name = NULL;
    RangeVar *label_range_var = NULL;
    Alias *alias = NULL;
    int resno = -1;
    TargetEntry *te = NULL;
    transform_entity *entity = NULL;
    cypher_relationship *cr = NULL;
    Node *expr = NULL;
    Var *previous_clause_var = NULL;
    bool refs_var = false;
    ParseNamespaceItem *pnsi = NULL;

    /*
     * If we have an edge name, get any potential variable or column
     * references. Additionally, verify that they are for edges.
     */
    if (rel->name != NULL)
    {
        te = findTarget(*target_list, rel->name);
        entity = find_variable(cpstate, rel->name);
        previous_clause_var = (Var *)colNameToVar(pstate, rel->name, false,
                                                  rel->location);

        /*
         * If we have a valid entity and te for this rel name, go ahead and get
         * the cypher relationship as we will need this for later and flag that
         * we have a variable reference.
         */
        if ((te != NULL && entity != NULL) ||
            (entity != NULL && previous_clause_var != NULL))
        {
            cr = (cypher_relationship *)entity->entity.rel;
            refs_var = true;
        }

        /* If the variable already exists, verify that it is for an edge */
        if (refs_var)
        {
            if (entity->type == ENT_VERTEX)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for a vertex", rel->name),
                        parser_errposition(pstate, rel->location)));
            }
            else if (entity->type == ENT_VLE_EDGE)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for a VLE edge", rel->name),
                        parser_errposition(pstate, rel->location)));
            }
            else if (entity->type == ENT_PATH &&
                     pstate->p_expr_kind != EXPR_KIND_SELECT_TARGET)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for a path", rel->name),
                        parser_errposition(pstate, rel->location)));
            }
        }

        else if (te && !entity)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_ALIAS),
                     errmsg("variable '%s' already exists", rel->name),
                     parser_errposition(pstate, rel->location)));
        }
    }

    /*
     * If we do not have a label for this edge, we either need to find one
     * from a referenced variable or we need to set it to the default label.
     */
    if (rel->label == NULL)
    {
        /* if there is a variable for this rel name */
        if (refs_var)
        {
            /*
             * If the referenced var has a non NULL label, copy it. This is
             * usually the case when it uses a variable that is already defined.
             * Fx -
             *
             *     MATCH (u:people)-[e:knows]->(v:people), (v)-[e]->(u) RETURN e
             *     MATCH (u:people)-[]->()-[]->(u) RETURN u
             *
             * We copy it so that we know what label it is referencing.
             */
            if (cr->parsed_label != NULL)
            {
                rel->parsed_label = cr->parsed_label;
                rel->label = cr->label;
            }
            else
            {
                rel->label = AG_DEFAULT_LABEL_EDGE;
            }
        }
        /* otherwise, just give it the default label */
        else
        {
            rel->label = AG_DEFAULT_LABEL_EDGE;
        }
    }
    /* if we do have a label, is it valid */
    else if (!valid_label)
    {
        /*
         *  XXX: Need to determine proper rules, for when label does not exist
         *  or is for an vertex. Maybe labels and edges should share names, like
         *  in openCypher. But these are stand in errors, to prevent
         *  segmentation faults, and other errors.
         *
         *  Update: Nonexistent and mismatched labels now return a NULL value to
         *  prevent segmentation faults, and other errors. We can also consider
         *  if an all-purpose label would be useful.
         */
        rel->label = NULL;
    }

    /*
     * Variables for edges are not allowed to be used multiple times within the
     * same clause.
     */
    if (previous_clause_var == NULL && refs_var)
    {
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_ALIAS),
                 errmsg("duplicate edge variable '%s' within a clause",
                        rel->name),
                 parser_errposition(pstate, rel->location)));
    }

    /*
     * If this edge uses a variable that already exists, verify that the label
     * names are the same.
     */
    if (refs_var &&
        (cr->parsed_label != NULL || rel->parsed_label != NULL) &&
        (cr->parsed_label == NULL || rel->parsed_label == NULL ||
        (strcmp(cr->parsed_label, rel->parsed_label) != 0)))
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("multiple labels for variable '%s' are not supported",
                        rel->name),
                 parser_errposition(pstate, rel->location)));
    }

    /*
     * Now we need to do a few checks and either return the existing var or
     * or build a new edge.
     */
    if (rel->name != NULL)
    {
        /*
         * If we are in a WHERE clause transform, we don't want to create new
         * variables, we want to use the existing ones. So, error if otherwise.
         * If we are in a subquery transform, we are allowed to create new variables
         * in the match, and all variables outside are visible to
         * the subquery.
         */
        if (pstate->p_expr_kind == EXPR_KIND_WHERE &&
            cpstate->subquery_where_flag == false)
        {
            cypher_parsestate *parent_cpstate =
               (cypher_parsestate *)pstate->parentParseState->parentParseState;
            /*
             *  If expr_kind is WHERE, the expressions are in the parent's
             *  parent's parsestate, due to the way we transform sublinks.
             */
            transform_entity *tentity = NULL;

            /* if we have the referenced var, just return it */
            if (previous_clause_var != NULL)
            {
                return (Expr *)previous_clause_var;
            }

            tentity = find_variable(parent_cpstate, rel->name);
            if (tentity != NULL)
            {
                return get_relative_expr(tentity, 2);
            }
            else
            {
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("variable `%s` does not exist", rel->name),
                         parser_errposition(pstate, rel->location)));
            }
        }

        /* if this vertex is referencing an existing te var, return its expr */
        if (refs_var)
        {
            return (te != NULL) ? te->expr : (Expr *)previous_clause_var;
        }
    }

    /* if we aren't using a variable, build the edge */
    if (!rel->name)
    {
        rel->name = get_next_default_alias(cpstate);
    }

    schema_name = get_graph_namespace_name(cpstate->graph_name);

    if (valid_label)
    {
        rel_name = get_label_relation_name(rel->label, cpstate->graph_oid);
    }
    else
    {
        rel_name = AG_DEFAULT_LABEL_EDGE;
    }

    label_range_var = makeRangeVar(schema_name, rel_name, -1);
    alias = makeAlias(rel->name, NIL);

    pnsi = addRangeTableEntry(pstate, label_range_var, alias,
                             label_range_var->inh, true);
    Assert(pnsi != NULL);

    /*
     * relation is visible (r.a in expression works) but attributes in the
     * relation are not visible (a in expression doesn't work)
     */
    addNSItemToQuery(pstate, pnsi, true, true, false);

    resno = pstate->p_next_resno++;

    if (valid_label)
    {
        expr = make_edge_expr(cpstate, pnsi);
    }
    else
    {
        expr = (Node *)makeNullConst(AGTYPEOID, -1, InvalidOid);
    }

    if (rel->name)
    {
        te = makeTargetEntry((Expr *)expr, resno, rel->name, false);
        *target_list = lappend(*target_list, te);
    }

    return (Expr *)expr;
}

static Expr *transform_cypher_node(cypher_parsestate *cpstate,
                                   cypher_node *node, List **target_list,
                                   bool output_node, bool valid_label)
{
    ParseState *pstate = (ParseState *)cpstate;
    char *schema_name = NULL;
    char *rel_name = NULL;
    RangeVar *label_range_var = NULL;
    Alias *alias = NULL;
    int resno = -1;
    TargetEntry *te = NULL;
    Expr *expr = NULL;
    transform_entity *entity = NULL;
    cypher_node *cn = NULL;
    bool refs_var = false;
    ParseNamespaceItem *pnsi = NULL;
    Var *previous_clause_var = NULL;

    /* if we have a node name, get any potential variable references */
    if (node->name != NULL)
    {
        te = findTarget(*target_list, node->name);
        entity = find_variable(cpstate, node->name);
        previous_clause_var = (Var *)colNameToVar(pstate, node->name, false,
                                                  node->location);

        /*
         * If we have a valid entity and te or a valid entity and a previous var
         * ref for this rel name, go ahead and get the cypher relationship. We
         * will need this information for later. Additionally, flag that we have
         * a variable reference.
         */
        if ((te != NULL && entity != NULL) ||
            (entity != NULL && previous_clause_var != NULL))
        {
            cn = (cypher_node *)entity->entity.node;
            refs_var = true;
        }

        /* If the variable already exists, verify that it is for a vertex */
        if (refs_var)
        {
            if (entity->type == ENT_EDGE)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for an edge", node->name),
                        parser_errposition(pstate, node->location)));
            }
            else if (entity->type == ENT_VLE_EDGE)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for a VLE edge", node->name),
                        parser_errposition(pstate, node->location)));
            }
            /* gets non EXISTS cases */
            else if (entity->type == ENT_PATH &&
                     pstate->p_expr_kind != EXPR_KIND_SELECT_TARGET)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("variable '%s' is for a path", node->name),
                        parser_errposition(pstate, node->location)));
            }
            /* gets EXISTS cases */
            else if (entity->type == ENT_PATH &&
                     pstate->p_expr_kind == EXPR_KIND_SELECT_TARGET)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_DUPLICATE_ALIAS),
                        errmsg("a path variable '%s' is not allowed here",
                               node->name),
                        parser_errposition(pstate, node->location)));
            }
        }

        /* If their is a te but no entity, it implies that their is
         * some variable that exists but not an edge,vle or a vertex
         */
        else if (te && !entity)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_ALIAS),
                     errmsg("variable '%s' already exists", node->name),
                     parser_errposition(pstate, node->location)));
        }
    }

    /*
     * If we do not have a label for this vertex, we either need to find one
     * from a referenced variable or we need to set it to the default label.
     */
    if (node->label == NULL)
    {
        if (refs_var)
        {
            /*
             * If the referenced var has a non NULL label, copy it. This is
             * usually the case when it uses a variable that is already defined.
             * Fx -
             *
             *     MATCH (u:people)-[e:knows]->(v:people), (v)-[e]->(u) RETURN e
             *     MATCH (u:people)-[]->()-[]->(u) RETURN u
             *
             * We copy it so that we know what label it is referencing.
             */
            if (cn->parsed_label != NULL)
            {
                node->parsed_label = cn->parsed_label;
                node->label = cn->label;
            }
            else
            {
                node->label = AG_DEFAULT_LABEL_VERTEX;
            }
        }
        /* otherwise, just give it the default label */
        else
        {
            node->label = AG_DEFAULT_LABEL_VERTEX;
        }
    }
    /* if we do have a label, is it valid */
    else if (!valid_label)
    {
        /*
         *  XXX: Need to determine proper rules, for when label does not exist
         *  or is for an edge. Maybe labels and edges should share names, like
         *  in openCypher. But these are stand in errors, to prevent
         *  segmentation faults, and other errors.
         *
         *  Update: Nonexistent and mismatched labels now return a NULL value to
         *  prevent segmentation faults, and other errors. We can also consider
         *  if an all-purpose label would be useful.
         */
        node->label = NULL;
    }

    /*
     * If this vertex uses a variable that already exists, verify that the label
     * being used is of the same name.
     */
    if (refs_var &&
        (cn->parsed_label != NULL || node->parsed_label != NULL) &&
        (cn->parsed_label == NULL || node->parsed_label == NULL ||
        (strcmp(cn->parsed_label, node->parsed_label) != 0)))
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("multiple labels for variable '%s' are not supported",
                        node->name),
                 parser_errposition(pstate, node->location)));
    }

    /* if it is not an output node, just return null */
    if (!output_node)
    {
        return NULL;
    }

    /*
     * Now we need to do a few checks and either return the existing var or
     * or build a new vertex.
     */
    if (node->name != NULL)
    {
        Node *expr = NULL;

        /*
         * If we are in a WHERE clause transform, we don't want to create new
         * variables, we want to use the existing ones. So, error if otherwise.
         * If we are in a subquery transform, we are allowed to create new variables
         * in the match, and all variables outside are visible to
         * the subquery.
         */
        if (pstate->p_expr_kind == EXPR_KIND_WHERE &&
            cpstate->subquery_where_flag == false)
        {
            cypher_parsestate *parent_cpstate =
               (cypher_parsestate *)pstate->parentParseState->parentParseState;
            bool is_vle = false;

            /*
             *  If expr_kind is WHERE, the expressions are in the parent's
             *  parent's parsestate, due to the way we transform sublinks.
             */
            transform_entity *tentity = NULL;

            /* if we have the referenced var, just return it */
            if (previous_clause_var != NULL)
            {
                return (Expr *)previous_clause_var;
            }

            tentity = find_variable(parent_cpstate, node->name);
            if (tentity != NULL)
            {
                return get_relative_expr(tentity, 2);
            }

            /*
             * Is this a VLE end node? We check this now in case it did exist
             * outside of the WHERE clause. In that case we would want to
             * process it normally.
             */
            is_vle = (strncmp(node->name,
                              AGE_DEFAULT_PREFIX"vle_function_end_var",
                              strlen(AGE_DEFAULT_PREFIX"vle_function_end_var"))
                      == 0);

            /*
             * The vle end node is an exception and needs to be created if it
             * doesn't exist. So fall through for it, otherwise error out.
             */
            if (!is_vle)
            {
                ereport(ERROR,
                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                        errmsg("variable `%s` does not exist", node->name),
                        parser_errposition(pstate, node->location)));
            }
        }

        /* if this vertex is referencing an existing var, return its expr */
        if (refs_var)
        {
            return (te != NULL) ? te->expr : (Expr *)previous_clause_var;
        }

        /* if this vertex is referencing an existing col var, return its expr */
        expr = colNameToVar(pstate, node->name, false, node->location);
        if (expr != NULL)
        {
            return (Expr*)expr;
        }
    }
    else
    {
        node->name = get_next_default_alias(cpstate);
    }

    /* now build a new vertex */
    schema_name = get_graph_namespace_name(cpstate->graph_name);

    if (valid_label)
    {
        rel_name = get_label_relation_name(node->label, cpstate->graph_oid);
    }
    else
    {
        rel_name = AG_DEFAULT_LABEL_VERTEX;
    }

    label_range_var = makeRangeVar(schema_name, rel_name, -1);
    alias = makeAlias(node->name, NIL);

    pnsi = addRangeTableEntry(pstate, label_range_var, alias,
                             label_range_var->inh, true);

    Assert(pnsi != NULL);

    /*
     * relation is visible (r.a in expression works) but attributes in the
     * relation are not visible (a in expression doesn't work)
     */
    addNSItemToQuery(pstate, pnsi, true, true, true);

    resno = pstate->p_next_resno++;

    if (valid_label)
    {
        expr = (Expr *)make_vertex_expr(cpstate, pnsi);
    }
    else
    {
        expr = (Expr*)makeNullConst(AGTYPEOID, -1, InvalidOid);
    }

    /* make target entry and add it */
    te = makeTargetEntry(expr, resno, node->name, false);
    *target_list = lappend(*target_list, te);

    return expr;
}

static Node *make_edge_expr(cypher_parsestate *cpstate,
                            ParseNamespaceItem *pnsi)
{
    ParseState *pstate = (ParseState *)cpstate;
    Oid label_name_func_oid;
    Oid func_oid;
    Node *id, *start_id, *end_id;
    Const *graph_oid_const;
    Node *props;
    List *args, *label_name_args;
    FuncExpr *func_expr;
    FuncExpr *label_name_func_expr;

    func_oid = get_ag_func_oid("_agtype_build_edge", 5, GRAPHIDOID, GRAPHIDOID,
                               GRAPHIDOID, CSTRINGOID, AGTYPEOID);

    id = scanNSItemForColumn(pstate, pnsi, 0, AG_EDGE_COLNAME_ID, -1);

    start_id = scanNSItemForColumn(pstate, pnsi, 0, AG_EDGE_COLNAME_START_ID, -1);

    end_id = scanNSItemForColumn(pstate, pnsi, 0, AG_EDGE_COLNAME_END_ID, -1);

    label_name_func_oid = get_ag_func_oid("_label_name", 2, OIDOID,
                                          GRAPHIDOID);

    graph_oid_const = makeConst(OIDOID, -1, InvalidOid, sizeof(Oid),
                                ObjectIdGetDatum(cpstate->graph_oid), false,
                                true);

    label_name_args = list_make2(graph_oid_const, id);

    label_name_func_expr = makeFuncExpr(label_name_func_oid, CSTRINGOID,
                                        label_name_args, InvalidOid,
                                        InvalidOid, COERCE_EXPLICIT_CALL);
    label_name_func_expr->location = -1;

    props = scanNSItemForColumn(pstate, pnsi, 0, AG_EDGE_COLNAME_PROPERTIES, -1);

    args = list_make4(id, start_id, end_id, label_name_func_expr);
    args = lappend(args, props);

    func_expr = makeFuncExpr(func_oid, AGTYPEOID, args, InvalidOid, InvalidOid,
                             COERCE_EXPLICIT_CALL);
    func_expr->location = -1;

    return (Node *)func_expr;
}
static Node *make_vertex_expr(cypher_parsestate *cpstate,
                              ParseNamespaceItem *pnsi)
{
    ParseState *pstate = (ParseState *)cpstate;
    Oid label_name_func_oid;
    Oid func_oid;
    Node *id;
    Const *graph_oid_const;
    Node *props;
    List *args, *label_name_args;
    FuncExpr *func_expr;
    FuncExpr *label_name_func_expr;

    Assert(pnsi != NULL);

    func_oid = get_ag_func_oid("_agtype_build_vertex", 3, GRAPHIDOID,
                               CSTRINGOID, AGTYPEOID);

    id = scanNSItemForColumn(pstate, pnsi, 0, AG_VERTEX_COLNAME_ID, -1);

    label_name_func_oid = get_ag_func_oid("_label_name", 2, OIDOID,
                                          GRAPHIDOID);

    graph_oid_const = makeConst(OIDOID, -1, InvalidOid, sizeof(Oid),
                                ObjectIdGetDatum(cpstate->graph_oid), false,
                                true);

    label_name_args = list_make2(graph_oid_const, id);

    label_name_func_expr = makeFuncExpr(label_name_func_oid, CSTRINGOID,
                                        label_name_args, InvalidOid,
                                        InvalidOid, COERCE_EXPLICIT_CALL);
    label_name_func_expr->location = -1;

    props = scanNSItemForColumn(pstate, pnsi, 0, AG_VERTEX_COLNAME_PROPERTIES,
                                -1);

    args = list_make3(id, label_name_func_expr, props);

    func_expr = makeFuncExpr(func_oid, AGTYPEOID, args, InvalidOid, InvalidOid,
                             COERCE_EXPLICIT_CALL);
    func_expr->location = -1;

    return (Node *)func_expr;
}

static Query *transform_cypher_create(cypher_parsestate *cpstate,
                                      cypher_clause *clause)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_create *self = (cypher_create *)clause->self;
    cypher_create_target_nodes *target_nodes;
    Const *null_const;
    List *transformed_pattern;
    FuncExpr *func_expr;
    Query *query;
    TargetEntry *tle;

    target_nodes = make_ag_node(cypher_create_target_nodes);
    target_nodes->flags = CYPHER_CLAUSE_FLAG_NONE;
    target_nodes->graph_oid = cpstate->graph_oid;

    query = makeNode(Query);
    query->commandType = CMD_SELECT;
    query->targetList = NIL;

    if (clause->prev)
    {
        handle_prev_clause(cpstate, query, clause->prev, true);

        target_nodes->flags |= CYPHER_CLAUSE_FLAG_PREVIOUS_CLAUSE;
    }

    null_const = makeNullConst(AGTYPEOID, -1, InvalidOid);
    tle = makeTargetEntry((Expr *)null_const, pstate->p_next_resno++,
                          AGE_VARNAME_CREATE_NULL_VALUE, false);
    query->targetList = lappend(query->targetList, tle);

    /*
     * Create the Const Node to hold the pattern. skip the parse node,
     * because we would not be able to control how our pointer to the
     * internal type is copied.
     */
    transformed_pattern = transform_cypher_create_pattern(cpstate, query,
                                                          self->pattern);

    target_nodes->paths = transformed_pattern;
    if (!clause->next)
    {
        target_nodes->flags |= CYPHER_CLAUSE_FLAG_TERMINAL;
    }


    func_expr = make_clause_func_expr(CREATE_CLAUSE_FUNCTION_NAME,
                                      (Node *)target_nodes);

    /* Create the target entry */
    tle = makeTargetEntry((Expr *)func_expr, pstate->p_next_resno++,
                          AGE_VARNAME_CREATE_CLAUSE, false);
    query->targetList = lappend(query->targetList, tle);

    query->rtable = pstate->p_rtable;
    query->rteperminfos = pstate->p_rteperminfos;
    query->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    query->hasAggs = pstate->p_hasAggs;
    query->hasSubLinks = pstate->p_hasSubLinks;

    return query;
}

static List *transform_cypher_create_pattern(cypher_parsestate *cpstate,
                                             Query *query, List *pattern)
{
    ListCell *lc;
    List *transformed_pattern = NIL;

    foreach (lc, pattern)
    {
        cypher_create_path *transformed_path;

        transformed_path = transform_cypher_create_path(cpstate,
                                                        &query->targetList,
                                                        lfirst(lc));

        transformed_pattern = lappend(transformed_pattern, transformed_path);
    }

    return transformed_pattern;
}

static cypher_create_path *
transform_cypher_create_path(cypher_parsestate *cpstate, List **target_list,
                             cypher_path *path)
{
    ParseState *pstate = (ParseState *)cpstate;
    ListCell *lc, *prev_node = NULL;
    List *transformed_path = NIL;
    cypher_create_path *ccp = make_ag_node(cypher_create_path);
    bool in_path = path->var_name != NULL;

    ccp->path_attr_num = InvalidAttrNumber;

    if (in_path)
    {
        if (findTarget(*target_list, path->var_name) != NULL)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_ALIAS),
                     errmsg("variable \"%s\" already exists",
                            path->var_name),
                     parser_errposition(pstate, path->location)));
        }
    }

    foreach (lc, path->path)
    {
        if (is_ag_node(lfirst(lc), cypher_node))
        {
            cypher_node *node = lfirst(lc);
            transform_entity *entity;
            ListCell *next_node = lnext(path->path, lc);

            cypher_target_node *rel =
                transform_create_cypher_node(cpstate, target_list, node,
                                             (next_node || prev_node));

            if (in_path)
            {
                if (node->name && strcmp(node->name, path->var_name) == 0)
                {
                    ereport(ERROR,
                            (errcode(ERRCODE_DUPLICATE_ALIAS),
                             errmsg("variable \"%s\" already exists",
                                    path->var_name),
                             parser_errposition(pstate, path->location)));
                }
                rel->flags |= CYPHER_TARGET_NODE_IN_PATH_VAR;
            }

            transformed_path = lappend(transformed_path, rel);

            entity = make_transform_entity(cpstate, ENT_VERTEX, (Node *)node,
                                           NULL);

            cpstate->entities = lappend(cpstate->entities, entity);
        }
        else if (is_ag_node(lfirst(lc), cypher_relationship))
        {
            cypher_relationship *edge = lfirst(lc);
            transform_entity *entity;

            cypher_target_node *rel =
                transform_create_cypher_edge(cpstate, target_list, edge);

            if (in_path)
            {
                if (edge->name && strcmp(edge->name, path->var_name) == 0)
                {
                    ereport(ERROR,
                            (errcode(ERRCODE_DUPLICATE_ALIAS),
                             errmsg("variable \"%s\" already exists",
                                    path->var_name),
                             parser_errposition(pstate, path->location)));
                }
                rel->flags |= CYPHER_TARGET_NODE_IN_PATH_VAR;
            }

            transformed_path = lappend(transformed_path, rel);

            entity = make_transform_entity(cpstate, ENT_EDGE, (Node *)edge,
                                           NULL);

            cpstate->entities = lappend(cpstate->entities, entity);
        }
        else
        {
            ereport(ERROR,
                    (errmsg_internal("unrecognized node in create pattern")));
        }
        prev_node = lc;
    }

    ccp->target_nodes = transformed_path;

    /*
     * If this path a variable, create a placeholder entry that we can fill
     * in with during the execution phase.
     */
    if (path->var_name)
    {
        TargetEntry *te;

        if (list_length(transformed_path) < 1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("paths require at least 1 vertex"),
                     parser_errposition(pstate, path->location)));
        }

        te = placeholder_target_entry(cpstate, path->var_name);

        ccp->path_attr_num = te->resno;

        *target_list = lappend(*target_list, te);
    }

    return ccp;
}

static cypher_target_node *
transform_create_cypher_edge(cypher_parsestate *cpstate, List **target_list,
                             cypher_relationship *edge)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_target_node *rel = make_ag_node(cypher_target_node);
    Expr *props;
    Relation label_relation;
    RangeVar *rv;
    RTEPermissionInfo *rte_pi;
    TargetEntry *te;
    char *alias;
    AttrNumber resno;
    ParseNamespaceItem *pnsi;

    if (edge->label)
    {
        if (get_label_kind(edge->label, cpstate->graph_oid) == LABEL_KIND_VERTEX)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("label %s is for vertices, not edges", edge->label),
                     parser_errposition(pstate, edge->location)));
        }
    }

    rel->type = LABEL_KIND_EDGE;
    rel->flags = CYPHER_TARGET_NODE_FLAG_INSERT;
    rel->label_name = edge->label;
    rel->resultRelInfo = NULL;

    if (edge->name)
    {
        /*
         * Variables can be declared in a CREATE clause, but not used if
         * it already exists.
         */
        transform_entity *entity;

        entity = find_variable(cpstate, edge->name);

        if (entity || variable_exists(cpstate, edge->name))
        {
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("variable %s already exists", edge->name),
                         parser_errposition(pstate, edge->location)));
        }

        rel->variable_name = edge->name;
        te = placeholder_target_entry(cpstate, edge->name);
        rel->tuple_position = te->resno;
        *target_list = lappend(*target_list, te);

        rel->flags |= CYPHER_TARGET_NODE_IS_VAR;
    }
    else
    {
        rel->variable_name = NULL;
        rel->tuple_position = 0;
    }

    if (edge->dir == CYPHER_REL_DIR_NONE)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("only directed relationships are allowed in CREATE"),
                 parser_errposition(&cpstate->pstate, edge->location)));
    }

    rel->dir = edge->dir;

    if (!edge->label)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("relationships must be specify a label in CREATE."),
                 parser_errposition(&cpstate->pstate, edge->location)));
    }

    /* create the label entry if it does not exist */
    if (!label_exists(edge->label, cpstate->graph_oid))
    {
        List *parent;

        rv = get_label_range_var(cpstate->graph_name, cpstate->graph_oid,
                                 AG_DEFAULT_LABEL_EDGE);

        parent = list_make1(rv);

        create_label(cpstate->graph_name, edge->label, LABEL_TYPE_EDGE,
                     parent);
    }

    /* lock the relation of the label */
    rv = makeRangeVar(cpstate->graph_name, edge->label, -1);
    label_relation = parserOpenTable(&cpstate->pstate, rv, RowExclusiveLock);

    /* Store the relid */
    rel->relid = RelationGetRelid(label_relation);

    pnsi = addRangeTableEntryForRelation((ParseState *)cpstate, label_relation,
                                        AccessShareLock, NULL, false, false);

    rte_pi = pnsi->p_perminfo;
    rte_pi->requiredPerms = ACL_INSERT;

    /* Build Id expression, always use the default logic */
    rel->id_expr = (Expr *)build_column_default(label_relation,
                                      Anum_ag_label_edge_table_id);

    /* Build properties expression, if no map is given, use the default logic */
    alias = get_next_default_alias(cpstate);
    resno = pstate->p_next_resno++;

    props = cypher_create_properties(cpstate, rel, label_relation, edge->props,
                                     ENT_EDGE);

    rel->prop_attr_num = resno - 1;
    te = makeTargetEntry(props, resno, alias, false);

    *target_list = lappend(*target_list, te);

    /* Keep the lock */
    table_close(label_relation, NoLock);

    return rel;
}

static bool variable_exists(cypher_parsestate *cpstate, char *name)
{
    ParseState *pstate = (ParseState *)cpstate;
    Node *id;
    ParseNamespaceItem *pnsi;

    if (name == NULL)
    {
        return false;
    }

    pnsi = find_pnsi(cpstate, PREV_CYPHER_CLAUSE_ALIAS);
    if (pnsi)
    {
        id = scanNSItemForColumn(pstate, pnsi, 0, name, -1);

        return id != NULL;
    }

    return false;
}

/* transform nodes, check to see if the variable name already exists. */
static cypher_target_node *
transform_create_cypher_node(cypher_parsestate *cpstate, List **target_list,
                             cypher_node *node, bool has_edge)
{
    ParseState *pstate = (ParseState *)cpstate;

    if (node->label)
    {
        if (get_label_kind(node->label, cpstate->graph_oid) == LABEL_KIND_EDGE)
        {
            ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                            errmsg("label %s is for edges, not vertices",
                                   node->label),
                            parser_errposition(pstate, node->location)));
        }
    }

    /*
     *  Check if the variable already exists, if so find the entity and
     *  setup the target node
     */
    if (node->name)
    {
        transform_entity *entity;

        TargetEntry *te = findTarget(*target_list, node->name);
        entity = find_variable(cpstate, node->name);

        /*
         * If we find an entity as well as a target Entry with same name,
         * that means that the variable is either vertex, edge or vle.
         * but if we find a target entry but not an entity that means
         * that the variable can be other than vertex, edge or vle e.g path.
         */
        if (entity && te)
        {
            if (entity->type != ENT_VERTEX || !has_edge)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("variable %s already exists", node->name),
                         parser_errposition(pstate, node->location)));
            }

            return transform_create_cypher_existing_node(cpstate, target_list,
                                                         entity->declared_in_current_clause, node);
        }
        else if (te)
        {
            if (!has_edge)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("variable %s already exists", node->name),
                         parser_errposition(pstate, node->location)));
            }
            /*
             * Here we are not sure if the te is a vertex, path or something
             * else. So we will let it pass and the execution stage will catch
             * the error if variable was not vertex.
             */
            return transform_create_cypher_existing_node(cpstate, target_list,
                                                         te, node);
        }
    }

    /* otherwise transform the target node as a new node */
    return transform_create_cypher_new_node(cpstate, target_list, node);
}

/*
 * Returns the resno for the TargetEntry with the resname equal to the name
 * passed. Returns -1 otherwise.
 */
static int get_target_entry_resno(List *target_list, char *name)
{
    ListCell *lc;

    foreach (lc, target_list)
    {
        TargetEntry *te = (TargetEntry *)lfirst(lc);
        if (!strcmp(te->resname, name))
        {
            return te->resno;
        }
    }

    return -1;
}

/* adds the volatile wrapper to the specified target entry */
static void add_volatile_wrapper_to_target_entry(List *target_list, int resno)
{
    ListCell *lc;

    Assert(target_list != NULL);
    Assert(resno >= 0);

    /* find the resource */
    foreach (lc, target_list)
    {
        TargetEntry *te = (TargetEntry *)lfirst(lc);
        if (te->resno == resno)
        {
            /* wrap it */
            te->expr = add_volatile_wrapper(te->expr);
            return;
        }
    }

    /* if we didn't find anything, there was a problem */
    ereport(ERROR,
            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
             errmsg("add_volatile_wrapper_to_target_entry: resno not found")));
}

/*
 * Transform logic for a previously declared variable in a CREATE clause.
 * All we need from the variable node is its id, and whether we can skip
 * some tests in the execution phase..
 */
static cypher_target_node *transform_create_cypher_existing_node(
    cypher_parsestate *cpstate, List **target_list, bool declared_in_current_clause,
    cypher_node *node)
{
    cypher_target_node *rel = make_ag_node(cypher_target_node);
    ParseState *pstate = (ParseState *)cpstate;

    rel->type = LABEL_KIND_VERTEX;
    rel->flags = CYPHER_TARGET_NODE_FLAG_NONE;
    rel->resultRelInfo = NULL;
    rel->variable_name = node->name;

    if (node->props)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("previously declared nodes in a create clause cannot have properties"),
                 parser_errposition(pstate, node->location)));
    }
    if (node->label)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("previously declared variables cannot have a label"),
                 parser_errposition(pstate, node->location)));
    }
    /*
     * When the variable is declared in the same clause this vertex is a part of
     * we can skip some expensive checks in the execution phase.
     */
    if (declared_in_current_clause)
    {
        rel->flags |= EXISTING_VARIABLE_DECLARED_SAME_CLAUSE;
    }

    /*
     * Get the AttrNumber the variable is stored in, so we can extract the id
     * later.
     */
    rel->tuple_position = get_target_entry_resno(*target_list, node->name);

    add_volatile_wrapper_to_target_entry(*target_list, rel->tuple_position);

    return rel;
}

/*
 * Transform logic for a node in a create clause that was not previously
 * declared.
 */
static cypher_target_node *
transform_create_cypher_new_node(cypher_parsestate *cpstate,
                                 List **target_list, cypher_node *node)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_target_node *rel = make_ag_node(cypher_target_node);
    Relation label_relation;
    RangeVar *rv;
    RTEPermissionInfo *rte_pi;
    TargetEntry *te;
    Expr *props;
    char *alias;
    int resno;
    ParseNamespaceItem *pnsi;

    rel->type = LABEL_KIND_VERTEX;
    rel->tuple_position = InvalidAttrNumber;
    rel->variable_name = NULL;
    rel->resultRelInfo = NULL;

    if (!node->label)
    {
        rel->label_name = "";
        /*
         *  If no label is specified, assign the generic label name that
         *  all labels are descendents of.
         */
        node->label = AG_DEFAULT_LABEL_VERTEX;
    }
    else
    {
        rel->label_name = node->label;
    }

    /* create the label entry if it does not exist */
    if (!label_exists(node->label, cpstate->graph_oid))
    {
        List *parent;

        rv = get_label_range_var(cpstate->graph_name, cpstate->graph_oid,
                                 AG_DEFAULT_LABEL_VERTEX);

        parent = list_make1(rv);

        create_label(cpstate->graph_name, node->label, LABEL_TYPE_VERTEX,
                     parent);
    }

    rel->flags = CYPHER_TARGET_NODE_FLAG_INSERT;

    rv = makeRangeVar(cpstate->graph_name, node->label, -1);
    label_relation = parserOpenTable(&cpstate->pstate, rv, RowExclusiveLock);

    /* Store the relid */
    rel->relid = RelationGetRelid(label_relation);

    pnsi = addRangeTableEntryForRelation((ParseState *)cpstate, label_relation,
                                        AccessShareLock, NULL, false, false);

    rte_pi = pnsi->p_perminfo;
    rte_pi->requiredPerms = ACL_INSERT;

    /* id */
    rel->id_expr = (Expr *)build_column_default(label_relation,
                                                Anum_ag_label_vertex_table_id);

    /* properties */
    alias = get_next_default_alias(cpstate);
    resno = pstate->p_next_resno++;

    props = cypher_create_properties(cpstate, rel, label_relation, node->props,
                                     ENT_VERTEX);

    rel->prop_attr_num = resno - 1;
    te = makeTargetEntry(props, resno, alias, false);
    *target_list = lappend(*target_list, te);

    table_close(label_relation, NoLock);

    if (node->name)
    {
        rel->variable_name = node->name;
        te = placeholder_target_entry(cpstate, node->name);
        rel->tuple_position = te->resno;
        *target_list = lappend(*target_list, te);
        rel->flags |= CYPHER_TARGET_NODE_IS_VAR;
    }
    else
    {
        node->name = get_next_default_alias(cpstate);
    }

    return rel;
}

/*
 * Variable Edges cannot be created until the executor phase, because we
 * don't know what their start and end node ids will be. Therefore, path
 * variables cannot be created either. Create a placeholder entry that we
 * will replace in the execution phase. Do this for nodes too, to be
 * consistent.
 */
static TargetEntry *placeholder_target_entry(cypher_parsestate *cpstate,
                                             char *name)
{
    ParseState *pstate = (ParseState *)cpstate;
    Expr *n;
    int resno;

    n = (Expr *)makeNullConst(AGTYPEOID, -1, InvalidOid);
    n = add_volatile_wrapper(n);

    resno = pstate->p_next_resno++;

    return makeTargetEntry(n, resno, name, false);
}

/*
 * Build the target list for an entity that is not a previously declared
 * variable.
 */
static Expr *cypher_create_properties(cypher_parsestate *cpstate,
                                      cypher_target_node *rel,
                                      Relation label_relation, Node *props,
                                      enum transform_entity_type type)
{
    Expr *properties;

    if (props != NULL && is_ag_node(props, cypher_param))
    {
        ParseState *pstate = (ParseState *) cpstate;
        cypher_param *param = (cypher_param *)props;

        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("properties in a CREATE clause as a parameter is not supported"),
                 parser_errposition(pstate, param->location)));
    }

    if (props)
    {
        ((cypher_map*)props)->keep_null = false;
        properties = (Expr *)transform_cypher_expr(cpstate, props,
                                                   EXPR_KIND_INSERT_TARGET);
    }
    else if (type == ENT_VERTEX)
    {
        properties = (Expr *)build_column_default(
            label_relation, Anum_ag_label_vertex_table_properties);
    }
    else if (type == ENT_EDGE)
    {
        properties = (Expr *)build_column_default(
            label_relation, Anum_ag_label_edge_table_properties);
    }
    else
    {
        ereport(ERROR, (errmsg_internal("unrecognized entity type")));
    }

    /* add a volatile wrapper call to prevent the optimizer from removing it */
    return (Expr *)add_volatile_wrapper(properties);
}

/*
 * This function is similar to transformFromClause() that is called with a
 * single RangeSubselect.
 */
static ParseNamespaceItem *
transform_cypher_clause_as_subquery(cypher_parsestate *cpstate,
                                    transform_method transform,
                                    cypher_clause *clause,
                                    Alias *alias,
                                    bool add_rte_to_query)
{
    ParseState *pstate = (ParseState *)cpstate;
    Query *query;
    RangeTblEntry *rte;
    ParseExprKind old_expr_kind = pstate->p_expr_kind;
    bool lateral = pstate->p_lateral_active;
    ParseNamespaceItem *pnsi;

    /*
     * We allow expression kinds of none, where, and subselect. Others MAY need
     * to be added depending. However, at this time, only these are needed.
     */
    Assert(pstate->p_expr_kind == EXPR_KIND_NONE ||
           pstate->p_expr_kind == EXPR_KIND_OTHER ||
           pstate->p_expr_kind == EXPR_KIND_WHERE ||
           pstate->p_expr_kind == EXPR_KIND_SELECT_TARGET ||
           pstate->p_expr_kind == EXPR_KIND_INSERT_TARGET ||
           pstate->p_expr_kind == EXPR_KIND_FROM_SUBSELECT);

    /*
     * As these are all sub queries, if this is just of type NONE, note it as a
     * SUBSELECT. Other types will be dealt with as needed.
     */
    if (pstate->p_expr_kind == EXPR_KIND_NONE)
    {
        pstate->p_expr_kind = EXPR_KIND_FROM_SUBSELECT;
    }
    else if (pstate->p_expr_kind == EXPR_KIND_OTHER)
    {
        /* this is a lateral subselect for the MERGE */
        pstate->p_expr_kind = EXPR_KIND_FROM_SUBSELECT;
        lateral = true;
    }
    /*
     * If this is a WHERE, pass it through and set lateral to true because it
     * needs to see what comes before it.
     */

    query = analyze_cypher_clause(transform, clause, cpstate);

    /* set pstate kind back */
    pstate->p_expr_kind = old_expr_kind;

    if (alias == NULL)
    {
        alias = makeAlias(PREV_CYPHER_CLAUSE_ALIAS, NIL);
    }

    pnsi = addRangeTableEntryForSubquery(pstate, query, alias, lateral, true);
    rte = pnsi->p_rte;

    /*
     * NOTE: skip namespace conflicts check if the rte will be the only
     *       RangeTblEntry in pstate
     */
    if (list_length(pstate->p_rtable) > 1)
    {
        List *namespace = NULL;
        int rtindex = 0;

        /* get the index of the last entry */
        rtindex = list_length(pstate->p_rtable);

        /* the rte at the end should be the rte just added */
        if (rte != rt_fetch(rtindex, pstate->p_rtable))
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rte must be last entry in p_rtable")));
        }

        namespace = list_make1(pnsi);

        checkNameSpaceConflicts(pstate, pstate->p_namespace, namespace);
    }

    if (add_rte_to_query)
    {
        /* all variables(attributes) from the previous clause(subquery) are visible */
        addNSItemToQuery(pstate, pnsi, true, false, true);
    }

    return pnsi;
}

/*
 * When we are done transforming a clause, before transforming the next clause
 * iterate through the transform entities and mark them as not belonging to
 * the clause that is currently being transformed.
 */
static void advance_transform_entities_to_next_clause(List *entities)
{
    ListCell *lc;

    foreach (lc, entities)
    {
        transform_entity *entity = lfirst(lc);

        entity->declared_in_current_clause = false;
    }
}

/*
 * Walk the clause chain and return true if any clause is a
 * data-modifying operation (CREATE, SET, DELETE, or MERGE).
 */
static bool clause_chain_has_dml(cypher_clause *clause)
{
    while (clause != NULL)
    {
        if (is_ag_node(clause->self, cypher_create) ||
            is_ag_node(clause->self, cypher_set) ||
            is_ag_node(clause->self, cypher_delete) ||
            is_ag_node(clause->self, cypher_merge))
        {
            return true;
        }

        clause = clause->prev;
    }

    return false;
}

/*
 * Build a false WHERE clause that forces a MATCH to return zero rows.
 * Used when the MATCH pattern references a label that does not exist.
 *
 * When volatile_needed is false, returns a constant (true = false) that
 * PG's planner may constant-fold -- this is fine when there is no DML
 * predecessor whose execution must be preserved.
 *
 * When volatile_needed is true, returns (random() IS NULL) instead.
 * random() is VOLATILE, so eval_const_expressions() cannot fold this,
 * preventing PG from creating a One-Time Filter: false that would
 * eliminate the DML predecessor scan without executing it.
 *
 * Note: AGE's add_volatile_wrapper() serves a similar anti-fold purpose
 * but operates at the Expr level (post-transform) and returns agtype,
 * so it cannot be used here in the parse-tree WHERE clause context.
 */
static Node *make_false_where_clause(bool volatile_needed)
{
    if (volatile_needed)
    {
        FuncCall *random_fn;
        NullTest *nt;

        random_fn = makeFuncCall(
            list_make2(makeString("pg_catalog"), makeString("random")),
            NIL,
            COERCE_EXPLICIT_CALL,
            -1);

        nt = makeNode(NullTest);
        nt->arg = (Expr *)random_fn;
        nt->nulltesttype = IS_NULL;
        nt->argisrow = false;
        nt->location = -1;

        return (Node *)nt;
    }
    else
    {
        cypher_bool_const *l = make_ag_node(cypher_bool_const);
        cypher_bool_const *r = make_ag_node(cypher_bool_const);

        l->boolean = true;
        l->location = -1;
        r->boolean = false;
        r->location = -1;

        return (Node *)makeSimpleA_Expr(AEXPR_OP, "=",
                                        (Node *)l, (Node *)r, -1);
    }
}

static Query *analyze_cypher_clause(transform_method transform,
                                    cypher_clause *clause,
                                    cypher_parsestate *parent_cpstate)
{
    cypher_parsestate *cpstate;
    Query *query;
    ParseState *parent_pstate = (ParseState*)parent_cpstate;
    ParseState *pstate;

    cpstate = make_cypher_parsestate(parent_cpstate);
    pstate = (ParseState*)cpstate;

    /* copy the expr_kind down to the child */
    pstate->p_expr_kind = parent_pstate->p_expr_kind;

    query = transform(cpstate, clause);

    advance_transform_entities_to_next_clause(cpstate->entities);

    parent_cpstate->entities = list_concat(parent_cpstate->entities,
                                           cpstate->entities);

    free_cypher_parsestate(cpstate);

    return query;
}

static TargetEntry *findTarget(List *targetList, char *resname)
{
    ListCell *lt;
    TargetEntry *te = NULL;

    if (resname == NULL)
    {
        return NULL;
    }

    foreach (lt, targetList)
    {
        te = lfirst(lt);

        if (te->resjunk)
        {
            continue;
        }

        if (strcmp(te->resname, resname) == 0)
        {
            return te;
        }
    }

    return NULL;
}

/*
 * Wrap the expression with a volatile function, to prevent the optimizer from
 * eliminating the expression.
 */
static Expr *add_volatile_wrapper(Expr *node)
{
    Oid oid;

    /* if the passed Expr node is NULL it will cause a crash, so notify us */
    if (node == NULL)
    {
        ereport(ERROR, (errmsg_internal("add_volatile_wrapper: NULL expr")));
    }

    oid = get_ag_func_oid("agtype_volatile_wrapper", 1, ANYOID);

    /* if the passed Expr node is already wrapped, just return it */
    if (IsA(node, FuncExpr) && oid == ((FuncExpr*)node)->funcid)
    {
        return node;
    }

    return (Expr *)makeFuncExpr(oid, AGTYPEOID, list_make1(node), InvalidOid,
                                InvalidOid, COERCE_EXPLICIT_CALL);
}

/*
 * from postgresql parse_sub_analyze
 * Modified entry point for recursively analyzing a sub-statement in union.
 */
Query *cypher_parse_sub_analyze_union(cypher_clause *clause,
                                      cypher_parsestate *cpstate,
                                      CommonTableExpr *parentCTE,
                                      bool locked_from_parent,
                                      bool resolve_unknowns)
{
    cypher_parsestate *state = make_cypher_parsestate(cpstate);
    Query *query;

    state->pstate.p_parent_cte = parentCTE;
    state->pstate.p_locked_from_parent = locked_from_parent;
    state->pstate.p_resolve_unknowns = resolve_unknowns;

    query = transform_cypher_clause(state, clause);

    free_cypher_parsestate(state);

    return query;
}

/*
 * from postgresql parse_sub_analyze
 * Entry point for recursively analyzing a sub-statement.
 */
Query *cypher_parse_sub_analyze(Node *parseTree,
                                cypher_parsestate *cpstate,
                                CommonTableExpr *parentCTE,
                                bool locked_from_parent,
                                bool resolve_unknowns)
{
    ParseState *pstate = make_parsestate((ParseState*)cpstate);
    cypher_clause *clause;
    Query *query;

    if (IsA(parseTree, Query))
    {
        /* Already transformed, just return it */
        return (Query *)parseTree;
    }

    pstate->p_parent_cte = parentCTE;
    pstate->p_locked_from_parent = locked_from_parent;
    pstate->p_resolve_unknowns = resolve_unknowns;

    clause = palloc0(sizeof(cypher_clause));
    clause->self = parseTree;
    query = transform_cypher_clause(cpstate, clause);

    free_parsestate(pstate);

    return query;
}

/*
 * Function for transforming MERGE.
 *
 * There are two cases for the form Query that is returned from here will
 * take:
 *
 * 1. If there is no previous clause, the query will have a subquery that
 * represents the path as a select statement, similar to match with a targetList
 * that is all declared variables and the FuncExpr that represents the MERGE
 * clause with its needed metadata information, that will be caught in the
 * planner phase and converted into a path.
 *
 * 2. If there is a previous clause then the query will have two subqueries.
 * The first query will be for the previous clause that we recursively handle.
 * The second query will be for the path that this MERGE clause defines. The
 * two subqueries will be joined together using a LATERAL LEFT JOIN with the
 * previous query on the left and the MERGE path subquery on the right. Like
 * case 1 the targetList will have all the declared variables and a FuncExpr
 * that represents the MERGE clause with its needed metadata information, that
 * will be caught in the planner phase and converted into a path.
 *
 * This will allow us to be capable of handling the 2 cases that exist with a
 * MERGE clause correctly.
 *
 * Case 1: the path already exists. In this case we do not need to create
 * the path and MERGE will simply pass the tuple information up the execution
 * tree.
 *
 * Case 2: the path does not exist. In this case the LEFT part of the join
 * will not prevent the tuples from the previous clause from being emitted. We
 * can catch when this happens in the execution phase and create the missing
 * data, before passing up the execution tree.
 *
 * It should be noted that both cases can happen in the same query. If the
 * MERGE clause references a variable from a previous clause, it could be that
 * for one tuple the path exists (or there is multiple paths that exist and all
 * paths must be emitted) and for another the path does not exist. This is
 * similar to OPTIONAL MATCH, however with the added feature of creating the
 * path if not there, rather than just emitting NULL.
 */
static Query *transform_cypher_merge(cypher_parsestate *cpstate,
                                     cypher_clause *clause)
{
    ParseState *pstate = (ParseState *) cpstate;
    cypher_clause *merge_clause_as_match;
    cypher_create_path *merge_path;
    cypher_merge *self = (cypher_merge *)clause->self;
    cypher_merge_information *merge_information;
    Query *query;
    FuncExpr *func_expr;
    TargetEntry *tle;

    Assert(is_ag_node(self->path, cypher_path));

    merge_information = make_ag_node(cypher_merge_information);

    query = makeNode(Query);
    query->commandType = CMD_SELECT;
    query->targetList = NIL;

    merge_information->flags = CYPHER_CLAUSE_FLAG_NONE;

    /* make the merge node into a match node */
    merge_clause_as_match = convert_merge_to_match(self);

    /*
     * If there is a previous clause we need to turn this query into a lateral
     * join. See the function transform_merge_make_lateral_join for details.
     */
    if (clause->prev != NULL)
    {
        merge_path = transform_merge_make_lateral_join(cpstate, query, clause,
                                                       merge_clause_as_match);

        merge_information->flags |= CYPHER_CLAUSE_FLAG_PREVIOUS_CLAUSE;
    }
    else
    {
        /* make the merge node into a match node */

        /* TODO this is called above and appears redundant but needs to be */
        /* looked into */
        /* cypher_clause *merge_clause_as_match = convert_merge_to_match(self); */

        /*
         * Create the metadata needed for creating missing paths.
         */
        merge_path = transform_cypher_merge_path(cpstate, &query->targetList,
                                                 (cypher_path *)self->path);

        /*
         * If there is not a previous clause, then treat the MERGE's path
         * itself as the previous clause. We need to do this because if the
         * pattern exists, then we need to path all paths that match the
         * query patterns in the execution phase. WE way to do that by
         * converting the merge to a match and have the match logic create the
         * query. the merge execution phase will just pass the results up the
         * execution tree if the path exists.
         */
        handle_prev_clause(cpstate, query, merge_clause_as_match, false);

        /*
         * For the metadata need to create paths, find the tuple position that
         * will represent the entity in the execution phase.
         */
        transform_cypher_merge_mark_tuple_position(cpstate, query->targetList,
                                                   merge_path);
    }

    merge_information->graph_oid = cpstate->graph_oid;
    merge_information->path = merge_path;

    if (!clause->next)
    {
        merge_information->flags |= CYPHER_CLAUSE_FLAG_TERMINAL;
    }

    /*
     * Creates the function expression that the planner will find and
     * convert to a MERGE path.
     */
    func_expr = make_clause_func_expr(MERGE_CLAUSE_FUNCTION_NAME,
                                      (Node *)merge_information);

    /* Create the target entry */
    tle = makeTargetEntry((Expr *)func_expr, pstate->p_next_resno++,
                          AGE_VARNAME_MERGE_CLAUSE, false);

    merge_information->merge_function_attr = tle->resno;
    query->targetList = lappend(query->targetList, tle);

    markTargetListOrigins(pstate, query->targetList);

    query->rtable = pstate->p_rtable;
    query->rteperminfos = pstate->p_rteperminfos;
    query->jointree = makeFromExpr(pstate->p_joinlist, NULL);
    query->hasAggs = pstate->p_hasAggs;
    query->hasSubLinks = pstate->p_hasSubLinks;

    assign_query_collations(pstate, query);

    return query;
}

/*
 * This function does the heavy lifting of transforming a MERGE clause that has
 * a clause before it in the query of turning that into a lateral left join.
 * The previous clause will still be able to emit tuples if the path defined in
 * MERGE clause is not found. In that case variable assigned in the MERGE
 * clause will be emitted as NULL (same as OPTIONAL MATCH).
 */
static cypher_create_path *
transform_merge_make_lateral_join(cypher_parsestate *cpstate, Query *query,
                                  cypher_clause *clause,
                                  cypher_clause *isolated_merge_clause)
{
    cypher_create_path *merge_path;
    ParseState *pstate = (ParseState *) cpstate;
    int i;
    Alias *l_alias;
    Alias *r_alias;
    RangeTblEntry *l_rte, *r_rte;
    ParseNamespaceItem *l_nsitem, *r_nsitem;
    JoinExpr *j = makeNode(JoinExpr);
    List *res_colnames = NIL, *res_colvars = NIL;
    ParseNamespaceItem *jnsitem;
    ParseExprKind tmp;
    cypher_merge *self = (cypher_merge *)clause->self;
    cypher_path *path;
    ListCell *lc;

    Assert(is_ag_node(self->path, cypher_path));

    path = (cypher_path *)self->path;

    r_alias = makeAlias(CYPHER_OPT_RIGHT_ALIAS, NIL);
    l_alias = makeAlias(PREV_CYPHER_CLAUSE_ALIAS, NIL);

    j->jointype = JOIN_LEFT;

    /*
     * transform the previous clause
     */
    j->larg = transform_clause_for_join(cpstate, clause->prev, &l_rte,
                                        &l_nsitem, l_alias);
    pstate->p_namespace = lappend(pstate->p_namespace, l_nsitem);

    /*
     * Get the merge path now. This is the only moment where it is simple
     * to know if a variable was declared in the MERGE clause or a previous
     * clause. Unlike create, we do not add these missing variables to the
     * targetList, we just create all the metadata necessary to make the
     * potentially missing parts of the path.
     */
    merge_path = transform_cypher_merge_path(cpstate, &query->targetList,
                                             path);

    /*
     * Transform this MERGE clause as a match clause, mark the parsestate
     * with the flag that a lateral join is active
     */
    pstate->p_lateral_active = true;
    tmp = pstate->p_expr_kind;
    pstate->p_expr_kind = EXPR_KIND_OTHER;

    /* transform MERGE */
    j->rarg = transform_clause_for_join(cpstate, isolated_merge_clause, &r_rte,
                                            &r_nsitem, r_alias);

    /*
     * Since this is a left join, we need to mark j->rarg as it may potentially
     * emit NULL. The jindex argument holds rtindex of the join's RTE, which is
     * created right after j->arg's RTE in this case.
     */
    markRelsAsNulledBy(pstate, j->rarg, r_nsitem->p_rtindex + 1);

    /* deactivate the lateral flag */
    pstate->p_lateral_active = false;

    pstate->p_namespace = NIL;

    /*
     * Resolve the column names and variables between the two subqueries,
     * in most cases, we can expect there to be overlap
     */
    get_res_cols(pstate, l_nsitem, r_nsitem, &res_colnames, &res_colvars);

    /* make the RTE for the join */
    jnsitem = addRangeTableEntryForJoin(pstate, res_colnames, NULL, j->jointype,
                                        0, res_colvars, NIL, NIL, j->alias,
                                        NULL, true);

    j->rtindex = jnsitem->p_rtindex;

    /*
     * The index of a node in the p_joinexpr list is expected to match the
     * rtindex the join expression is for. Add NULLs for all the previous
     * rtindexes and add the JoinExpr.
     */
    for (i = list_length(pstate->p_joinexprs) + 1; i < j->rtindex; i++)
    {
        pstate->p_joinexprs = lappend(pstate->p_joinexprs, NULL);
    }

    pstate->p_joinexprs = lappend(pstate->p_joinexprs, j);

    Assert(list_length(pstate->p_joinexprs) == j->rtindex);

    pstate->p_joinlist = lappend(pstate->p_joinlist, j);

    pstate->p_expr_kind = tmp;

    /* add jnsitem to column namespace only */
    addNSItemToQuery(pstate, jnsitem, false, true, true);

    /*
     * Create the targetList from the joined subqueries, add everything.
     */
    query->targetList = list_concat(query->targetList,
                                    make_target_list_from_join(pstate, jnsitem->p_rte));

    /*
     * Iterate through the targetList and wrap all user defined variables with a
     * volatile wrapper. This is necessary for allowing variables from previous
     * clauses to not be removed by the function remove_unused_subquery_outputs.
     * That function may replace variables, in place, with a NULL Const. We need
     * to fix them so that it doesn't. NOTE: Our hidden, internal vars, are not
     * wrapped.
     */
    foreach(lc, query->targetList)
    {
        TargetEntry *qte = (TargetEntry *)lfirst(lc);

        if (IsA(qte->expr, Var))
        {
            if (qte->resname != NULL &&
                pg_strncasecmp(qte->resname, AGE_DEFAULT_VARNAME_PREFIX,
                               strlen(AGE_DEFAULT_VARNAME_PREFIX)))
            {
                qte->expr = add_volatile_wrapper(qte->expr);
            }
        }
    }

    /*
     * For the metadata need to create paths, find the tuple position that
     * will represent the entity in the execution phase.
     */
    transform_cypher_merge_mark_tuple_position(cpstate, query->targetList,
                                               merge_path);

    return merge_path;
}

/*
 * Iterate through the path and find the TargetEntry in the target_list
 * that each cypher_target_node is referencing. Add the volatile wrapper
 * function to keep the optimizer from removing the TargetEntry.
 */
static void
transform_cypher_merge_mark_tuple_position(cypher_parsestate *cpstate,
                                           List *target_list,
                                           cypher_create_path *path)
{
    ListCell *lc = NULL;

    if (path->var_name)
    {
        TargetEntry *te = findTarget(target_list, path->var_name);

        /*
         * Add the volatile wrapper function around the expression, this
         * ensures the optimizer will not remove the expression, if nothing
         * other than a private data structure needs it.
         */
        te->expr = add_volatile_wrapper(te->expr);

        /* Mark the tuple position the target_node is for. */
        path->path_attr_num = te->resno;
    }

    foreach (lc, path->target_nodes)
    {
        cypher_target_node *node = lfirst(lc);

        TargetEntry *te = findTarget(target_list, node->variable_name);

        /*
         * Add the volatile wrapper function around the expression, this
         * ensures the optimizer will not remove the expression, if nothing
         * other than a private data structure needs it.
         */
        te->expr = add_volatile_wrapper(te->expr);

        /* Mark the tuple position the target_node is for. */
        node->tuple_position = te->resno;
    }

    /* Iterate through the entities wrapping Var nodes with the volatile
     * wrapper, if not already done.
     *
     * NOTE: add_volatile_wrapper function will not wrap itself so the following
     *       is safe to do.
     *
     * TODO: This ideally needs to be rewritten using a walker, to be more
     *       selective. However, walkers are tricky and take time to set up. For
     *       now, we brute force it. It is already restricted to explicitly
     *       named variables.
     *
     * TODO: We need to understand why add_volatile_wrapper is needed. Meaning,
     *       we need to understand why variables are removed by the function
     *       remove_unused_subquery_outputs. It "appears" that some linkage may
     *       not be set up properly, not allowing the PG logic to see that a
     *       variable is used from a previous clause. Right now, the volatile
     *       wrapper will suffice, but it is still a hack imho.
     *
     * TODO: There may be other locations where something similar may need to be
     *       done. This needs to be researched.
     */
    foreach (lc, cpstate->entities)
    {
        transform_entity *te = lfirst(lc);
        Node *node = (Node*) te->entity.node;
        char *name = NULL;

        if (is_ag_node(node, cypher_node))
        {
            name = te->entity.node->parsed_name;
        }
        else if (is_ag_node(node, cypher_relationship))
        {
            name = te->entity.rel->parsed_name;
        }
        else if (is_ag_node(node, cypher_path))
        {
            name = te->entity.path->parsed_var_name;
        }
        else
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DATA_EXCEPTION),
                     errmsg("unexpected transform_entity entity type")));
        }

        /* node needs to have a parsed_name, meaning a name from the query */
        if (name != NULL)
        {
            TargetEntry *tle = findTarget(target_list, name);

            if (tle != NULL && IsA(tle->expr, Var))
            {
                tle->expr = add_volatile_wrapper(tle->expr);
            }
        }
    }
}

/*
 * Helper function to return a shallow copy of an existing, already transformed,
 * matching variable. The copy returned will be flagged as such. If none are
 * found, it will return NULL. If it finds a mismatched type, it will error
 * stating that.
 */
static cypher_target_node *get_referenced_variable(ParseState *pstate,
                                                   Node *node,
                                                   List *transformed_path)
{
    ListCell *lc = NULL;
    char *node_name = NULL;
    char *node_label = NULL;
    char node_type = 0;
    int node_loc = -1;

    /* passed node should only be a vertex or an edge */
    Assert(is_ag_node(node, cypher_node) ||
           is_ag_node(node, cypher_relationship));

    /* set up our search based on our input type */
    if (is_ag_node(node, cypher_node))
    {
        node_name = ((cypher_node *)node)->name;
        node_label = ((cypher_node *)node)->label;
        node_loc = ((cypher_node *)node)->location;
        node_type = 'v';
    }
    else
    {
        node_name = ((cypher_relationship *)node)->name;
        node_label = ((cypher_relationship *)node)->label;
        node_loc = ((cypher_relationship *)node)->location;
        node_type = 'e';
    }

    /* look through the list of previously transformed nodes and edges */
    foreach (lc, transformed_path)
    {
        cypher_target_node *ctn = NULL;
        bool is_name = false;
        bool is_label = false;

        /* list items should be of type cypher_target_node */
        Assert(is_ag_node(lfirst(lc), cypher_target_node));
        ctn = lfirst(lc);

        /* do they have names? if so, do they match? */
        is_name = (node_name == NULL || ctn->variable_name == NULL) ?
            false : strcmp(node_name, ctn->variable_name) == 0;

        /* do they have labels? if so, do they match? */
        is_label = (ctn->label_name != NULL) ?
            ((node_label == NULL) ? true : strcmp(ctn->label_name, node_label) == 0)
            : false;

        /* if the types don't match, error or skip */
        if (node_type != ctn->type)
        {
            /* is the name a match, generate an error. otherwise, skip it. */
            if (is_name)
            {
                if (node_type == 'v')
                {
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("variable \"%s\" is for a edge",
                                    node_name),
                             parser_errposition(pstate, node_loc)));
                }
                else
                {
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("variable \"%s\" is for an vertex",
                                    node_name),
                             parser_errposition(pstate, node_loc)));
                }
            }
            else
            {
                continue;
            }
        }

        if (is_name && !is_label)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("multiple labels for variable '%s' are not supported",
                                    node_name),
                             parser_errposition(pstate, node_loc)));
        }

        /*
         * If this is a match, make a shallow copy of it, modify the copy to be
         * flagged as a previously declared variable, and then return it.
         */
        if (is_name && is_label)
        {
            cypher_target_node *_cpy = make_ag_node(cypher_target_node);

            /* make a shallow copy */
            _cpy->type = ctn->type;
            _cpy->flags = ctn->flags;
            _cpy->dir = ctn->dir;
            _cpy->id_expr = ctn->id_expr;
            _cpy->id_expr_state = ctn->id_expr_state;
            _cpy->prop_expr = ctn->prop_expr;
            _cpy->prop_expr_state = ctn->prop_expr_state;
            _cpy->prop_attr_num = ctn->prop_attr_num;
            _cpy->resultRelInfo = ctn->resultRelInfo;
            _cpy->elemTupleSlot = ctn->elemTupleSlot;
            _cpy->relid = ctn->relid;
            _cpy->label_name = ctn->label_name;
            _cpy->variable_name = ctn->variable_name;
            _cpy->tuple_position = ctn->tuple_position;

            /* set it to a declared variable */
            _cpy->flags &= 0xfffffffe;
            _cpy->flags |= EXISTING_VARIABLE_DECLARED_SAME_CLAUSE;

            return _cpy;
        }
    }
    return NULL;
}

/*
 * Creates the target nodes for a merge path. If MERGE has a path that doesn't
 * exist then in the MERGE clause we act like a CREATE clause. This function
 * sets up the metadata needed for that process.
 */
static cypher_create_path *
transform_cypher_merge_path(cypher_parsestate *cpstate, List **target_list,
                            cypher_path *path)
{
    ParseState *pstate = (ParseState *)cpstate;
    ListCell *lc, *prev_node = NULL;
    List *transformed_path = NIL;
    cypher_create_path *ccp = make_ag_node(cypher_create_path);
    bool in_path = path->var_name != NULL;

    ccp->path_attr_num = InvalidAttrNumber;

    foreach (lc, path->path)
    {
        if (is_ag_node(lfirst(lc), cypher_node))
        {
            cypher_node *node = lfirst(lc);
            cypher_target_node *rel = NULL;
            ListCell *next_node = lnext(path->path, lc);

            if (path->var_name != NULL && node->name != NULL &&
                strcmp(path->var_name, node->name) == 0)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("variable \"%s\" is for a path", node->name),
                         parser_errposition(pstate, node->location)));
            }

            /*
             * If the variable was already transformed, get a referenced copy of
             * it. This copy will make sure the executor phase doesn't create a
             * new node from it.
             */
            rel = get_referenced_variable(pstate, (Node *)node,
                                          transformed_path);

            /* if there wasn't a transformed variable, transform the node */
            if (rel == NULL)
            {
                rel = transform_merge_cypher_node(cpstate, target_list, node,
                                                  (next_node || prev_node));
            }

            if (in_path)
            {
                rel->flags |= CYPHER_TARGET_NODE_IN_PATH_VAR;
            }

            transformed_path = lappend(transformed_path, rel);
        }
        else if (is_ag_node(lfirst(lc), cypher_relationship))
        {
            cypher_relationship *edge = NULL;
            cypher_target_node *rel = NULL;

            edge = lfirst(lc);

            if (path->var_name != NULL && edge->name != NULL &&
                strcmp(path->var_name, edge->name) == 0)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("variable \"%s\" is for a path", edge->name),
                         parser_errposition(pstate, edge->location)));
            }

            /*
             * Get a referenced edge variable. This should not happen as edges
             * can not be duplicated within a path.
            */
            rel = get_referenced_variable(pstate, (Node *)edge,
                                          transformed_path);
            if (rel != NULL)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                                 errmsg("a duplicate edge variable \"%s\" is not permitted within a path",
                                        edge->name),
                                 parser_errposition(pstate, edge->location)));
            }

            /* transform the edge */
            rel = transform_merge_cypher_edge(cpstate, target_list, edge);

            if (in_path)
            {
                rel->flags |= CYPHER_TARGET_NODE_IN_PATH_VAR;
            }

            transformed_path = lappend(transformed_path, rel);
        }
        else
        {
            ereport(ERROR,
                    (errmsg_internal("unrecognized node in create pattern")));
        }
        prev_node = lc;
    }

    /* store the path's variable name */
    if (path->var_name)
    {
        ccp->var_name = path->var_name;
    }

    ccp->target_nodes = transformed_path;

    return ccp;
}

/*
 * Transforms the parse cypher_relationship to a target_entry for merge.
 * All edges that have variables assigned in a merge must be declared in
 * the merge. Throw an error otherwise.
 */
static cypher_target_node *
transform_merge_cypher_edge(cypher_parsestate *cpstate, List **target_list,
                             cypher_relationship *edge)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_target_node *rel = make_ag_node(cypher_target_node);
    Relation label_relation;
    RangeVar *rv;
    RTEPermissionInfo *rte_pi;
    ParseNamespaceItem *pnsi;

    if (edge->name != NULL)
    {
        transform_entity *entity = find_transform_entity(cpstate, edge->name,
                                                         ENT_EDGE);

        /* We found a variable with this variable name, throw an error. */
        if (entity || variable_exists(cpstate, edge->name))
        {
            ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("variable %s already exists", edge->name),
                 parser_errposition(pstate, edge->location)));
        }

        rel->flags |= CYPHER_TARGET_NODE_IS_VAR;
    }
    else
    {
        /* assign a default variable name. */
        edge->name = get_next_default_alias(cpstate);
    }

    rel->type = LABEL_KIND_EDGE;

    /* all edges are marked with insert */
    rel->flags |= CYPHER_TARGET_NODE_FLAG_INSERT;
    rel->label_name = edge->label;
    rel->variable_name = edge->name;
    rel->resultRelInfo = NULL;

    rel->dir = edge->dir;

    if (!edge->label)
    {
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("edges declared in a MERGE clause must have a label"),
                 parser_errposition(&cpstate->pstate, edge->location)));
    }


    /* check to see if the label exists, create the label entry if it does not. */
    if (edge->label && !label_exists(edge->label, cpstate->graph_oid))
    {
        List *parent;
        /*
         * setup the default edge table as the parent table, that we
         * will inherit from.
         */
        rv = get_label_range_var(cpstate->graph_name, cpstate->graph_oid,
                                 AG_DEFAULT_LABEL_EDGE);

        parent = list_make1(rv);

        /* create the label */
        create_label(cpstate->graph_name, edge->label, LABEL_TYPE_EDGE,
                     parent);
    }

    /* lock the relation of the label */
    rv = makeRangeVar(cpstate->graph_name, edge->label, -1);
    label_relation = parserOpenTable(&cpstate->pstate, rv, RowExclusiveLock);

    /*
     * TODO
     * It is possible for a vertex label to be retrieved, instead of an edge,
     * due to the above logic. So, we need to check if it is a vertex label.
     * This whole section needs to be fixed because it could be a relation that
     * isn't either and has the correct number of columns. However, for now,
     * we just check the number of columns.
     */
    /* TODO temporarily hardcoded */
    if (label_relation->rd_att->natts == 2)
    {
        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                        errmsg("Expecting edge label, found existing vertex label"),
                        parser_errposition(&cpstate->pstate, edge->location)));
    }

    /* Store the relid */
    rel->relid = RelationGetRelid(label_relation);

    pnsi = addRangeTableEntryForRelation((ParseState *)cpstate, label_relation,
                                         AccessShareLock, NULL, false, false);
    rte_pi = pnsi->p_perminfo;
    rte_pi->requiredPerms = ACL_INSERT;

    /* Build Id expression, always use the default logic */
    rel->id_expr = (Expr *)build_column_default(label_relation,
                                      Anum_ag_label_edge_table_id);

    rel->prop_expr = cypher_create_properties(cpstate, rel, label_relation,
                                              edge->props, ENT_EDGE);

    /* Keep the lock */
    table_close(label_relation, NoLock);

    return rel;
}

/*
 * Function for creating the metadata MERGE will need if MERGE does not find
 * a path to exist
 */
static cypher_target_node *
transform_merge_cypher_node(cypher_parsestate *cpstate, List **target_list,
                            cypher_node *node, bool has_edge)
{
    ParseState *pstate = (ParseState *)cpstate;
    cypher_target_node *rel = make_ag_node(cypher_target_node);
    Relation label_relation;
    RangeVar *rv;
    RTEPermissionInfo *rte_pi;
    ParseNamespaceItem *pnsi;

    if (node->name != NULL)
    {
        transform_entity *entity = find_transform_entity(cpstate, node->name,
                                                         ENT_VERTEX);
        bool var_exists = variable_exists(cpstate, node->name);
        /*
         *  the vertex was previously declared, we do not need to do any setup
         *  to create the node.
         */
        if (entity && var_exists)
        {
            if (!has_edge)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("variable %s already exists", node->name),
                         parser_errposition(pstate, node->location)));
            }

            rel->type = LABEL_KIND_VERTEX;
            rel->tuple_position = InvalidAttrNumber;
            rel->variable_name = node->name;
            rel->resultRelInfo = NULL;

            rel->flags |= CYPHER_TARGET_NODE_MERGE_EXISTS;
            return rel;
        }
        else if (var_exists && !has_edge)
        {
            ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("variable %s already exists", node->name),
                         parser_errposition(pstate, node->location)));
        }
        rel->flags |= CYPHER_TARGET_NODE_IS_VAR;
    }
    else
    {
        /* assign a default variable name. */
        node->name = get_next_default_alias(cpstate);
    }

    rel->type = LABEL_KIND_VERTEX;
    rel->tuple_position = InvalidAttrNumber;
    rel->variable_name = node->name;
    rel->resultRelInfo = NULL;

    if (!node->label)
    {
        rel->label_name = "";
        /*
         *  If no label is specified, assign the generic label name that
         *  all labels are descendents of.
         */
        node->label = AG_DEFAULT_LABEL_VERTEX;
    }
    else
    {
        rel->label_name = node->label;
    }

    /* check to see if the label exists, create the label entry if it does not. */
    if (node->label && !label_exists(node->label, cpstate->graph_oid))
    {
        List *parent;

        /*
         * setup the default vertex table as the parent table, that we
         * will inherit from.
         */
        rv = get_label_range_var(cpstate->graph_name, cpstate->graph_oid,
                                 AG_DEFAULT_LABEL_VERTEX);

        parent = list_make1(rv);

        /* create the label */
        create_label(cpstate->graph_name, node->label, LABEL_TYPE_VERTEX,
                     parent);
    }

    rel->flags |= CYPHER_TARGET_NODE_FLAG_INSERT;

    rv = makeRangeVar(cpstate->graph_name, node->label, -1);
    label_relation = parserOpenTable(&cpstate->pstate, rv, RowExclusiveLock);

    /*
     * TODO
     * It is possible for an edge label to be retrieved, instead of a vertex,
     * due to the above logic. So, we need to check if it is an edge label.
     * This whole section needs to be fixed because it could be a relation that
     * isn't either and has the correct number of columns. However, for now,
     * we just check the number of columns.
     */
     /* TODO temporarily hardcoded */
    if (label_relation->rd_att->natts == 4)
    {
        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                        errmsg("Expecting vertex label, found existing edge label"),
                        parser_errposition(&cpstate->pstate, node->location)));
    }

    /* Store the relid */
    rel->relid = RelationGetRelid(label_relation);

    pnsi = addRangeTableEntryForRelation((ParseState *)cpstate, label_relation,
                                         AccessShareLock, NULL, false, false);

    rte_pi = pnsi->p_perminfo;
    rte_pi->requiredPerms = ACL_INSERT;

    /* id */
    rel->id_expr = (Expr *)build_column_default(label_relation,
                                                Anum_ag_label_vertex_table_id);

    rel->prop_expr = cypher_create_properties(cpstate, rel, label_relation,
                                              node->props, ENT_VERTEX);

    table_close(label_relation, NoLock);

    return rel;
}

/*
 * Takes a MERGE parse node and converts it to a MATCH parse node
 */
static cypher_clause *convert_merge_to_match(cypher_merge *merge)
{
    cypher_match *match = make_ag_node(cypher_match);
    cypher_clause *clause = palloc(sizeof(cypher_clause));

    /* match supports multiple paths, whereas merge only supports one. */
    match->pattern = list_make1(merge->path);
    /* MERGE does not support where */
    match->where = NULL;

    /*
     *  We do not want the transform logic to transform the previous clauses
     *  with this, just handle this one clause.
     */
    clause->prev = NULL;
    clause->self = (Node *)match;
    clause->next = NULL;

    return clause;
}

/*
 * Creates a namespace item for the given rte. boolean arguments will
 * let the rest of the ParseState know if the relation and/or columns are
 * visible, whether the rte is only usable in lateral joins, and if the rte
 * is accessible in lateral joins.
 */
static ParseNamespaceItem *get_namespace_item(ParseState *pstate,
                                              RangeTblEntry *rte)
{
    ParseNamespaceItem *nsitem = NULL;
    ListCell *l;

    foreach(l, pstate->p_namespace)
    {
        nsitem = lfirst(l);
        if (rte == nsitem->p_rte)
        {
            return nsitem;
        }
    }
    Assert(nsitem != NULL);
    return NULL;
}

/*
 * Creates the function expression that represents the clause. Adds the
 * extensible node that represents the metadata that the clause needs to
 * handle the clause in the execution phase.
 */
static FuncExpr *make_clause_func_expr(char *function_name,
                                       Node *clause_information)
{
    Const *clause_information_const;
    Oid func_oid;
    FuncExpr *func_expr;

    StringInfo str = makeStringInfo();
    /*
     * Serialize the clause_information data structure. In certain
     * cases (Prepared Statements and PL/pgsql), the MemoryContext that
     * it is stored in will be destroyed. We need to get it into a format
     * that Postgres' can copy between MemoryContexts. Just making it into
     * an ExtensibleNode does not work, because there are certain parts of
     * Postgres that cannot handle an ExtensibleNode in a function call.
     * So we serialize the data structure and place it into a Const node
     * that can handle these situations AND be copied correctly.
     */
    outNode(str, clause_information);

    clause_information_const = makeConst(INTERNALOID, -1, InvalidOid, str->len,
                             PointerGetDatum(str->data), false, false);

    func_oid = get_ag_func_oid(function_name, 1, INTERNALOID);

    func_expr = makeFuncExpr(func_oid, AGTYPEOID,
                             list_make1(clause_information_const), InvalidOid,
                             InvalidOid, COERCE_EXPLICIT_CALL);

    return func_expr;
}

/*
 * This function is borrowed from PG version 16.1.
 *
 * It is used in transformations involving left join in Optional Match and
 * Merge in a similar way PG16's transformFromClauseItem() uses it.
 */
static void markRelsAsNulledBy(ParseState *pstate, Node *n, int jindex)
{
    int varno;
    ListCell *lc;

    /* Note: we can't see FromExpr here */
    if (IsA(n, RangeTblRef))
    {
        varno = ((RangeTblRef *) n)->rtindex;
    }
    else if (IsA(n, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) n;

        /* recurse to children */
        markRelsAsNulledBy(pstate, j->larg, jindex);
        markRelsAsNulledBy(pstate, j->rarg, jindex);
        varno = j->rtindex;
    }
    else
    {
        elog(ERROR, "unrecognized node type: %d", (int) nodeTag(n));
        varno = 0;				/* keep compiler quiet */
    }

    /*
     * Now add jindex to the p_nullingrels set for relation varno.  Since we
     * maintain the p_nullingrels list lazily, we might need to extend it to
     * make the varno'th entry exist.
     */
    while (list_length(pstate->p_nullingrels) < varno)
    {
        pstate->p_nullingrels = lappend(pstate->p_nullingrels, NULL);
    }
    lc = list_nth_cell(pstate->p_nullingrels, varno - 1);
    lfirst(lc) = bms_add_member((Bitmapset *) lfirst(lc), jindex);
}

/*
 * Utility function that helps a clause add the information needed to
 * the query from the previous clause.
 */
static void handle_prev_clause(cypher_parsestate *cpstate, Query *query,
                               cypher_clause *clause, bool first_rte)
{
    ParseState *pstate = (ParseState *) cpstate;
    int rtindex;
    ParseNamespaceItem *pnsi;

    pnsi = transform_prev_cypher_clause(cpstate, clause, true);

    rtindex = list_length(pstate->p_rtable);

    /* rte is the first RangeTblEntry in pstate */
    if (first_rte)
    {
        if (rtindex != 1)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("invalid value for rtindex")));
        }
    }

    /* add all the rte's attributes to the current queries targetlist */
    query->targetList = expandNSItemAttrs(pstate, pnsi, 0, true, -1);
}

ParseNamespaceItem *find_pnsi(cypher_parsestate *cpstate, char *varname)
{
    ParseState *pstate = (ParseState *) cpstate;
    ListCell *lc;

    foreach (lc, pstate->p_namespace)
    {
        ParseNamespaceItem *pnsi = (ParseNamespaceItem *)lfirst(lc);
        Alias *alias = pnsi->p_rte->alias;
        if (!alias)
        {
            continue;
        }

        if (!strcmp(alias->aliasname, varname))
        {
            return pnsi;
        }
    }

    return NULL;
}