feat(table-model): implement DESCRIBE QUERY for relational metadata extraction

Author: ShauryaChauhan1411

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/QueryExecution.java

@@ -252,7 +252,7 @@ private ExecutionResult retry() {
   }
 
   private boolean skipExecute() {
-    return analysis.canSkipExecute(context);
+    return analysis.isFailed() || analysis.isFinishQueryAfterAnalyze();
   }
 
   private void constructResultForMemorySource() {

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/memory/TableModelStatementMemorySourceVisitor.java

@@ -130,6 +130,61 @@ public StatementMemorySource visitCountDevice(
         node.getTsBlock(context.getAnalysis()), node.getDataSetHeader());
   }
 
+  @Override
+  public StatementMemorySource visitDescribeQuery(
+      org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeQuery node,
+      TableModelStatementMemorySourceContext context) {
+
+    java.util.List<org.apache.iotdb.commons.schema.column.ColumnHeader> columnHeaders =
+        new java.util.ArrayList<>();
+    columnHeaders.add(
+        new org.apache.iotdb.commons.schema.column.ColumnHeader(
+            "Column", org.apache.tsfile.enums.TSDataType.TEXT));
+    columnHeaders.add(
+        new org.apache.iotdb.commons.schema.column.ColumnHeader(
+            "Type", org.apache.tsfile.enums.TSDataType.TEXT));
+
+    org.apache.iotdb.db.queryengine.common.header.DatasetHeader datasetHeader =
+        new org.apache.iotdb.db.queryengine.common.header.DatasetHeader(columnHeaders, true);
+
+    java.util.List<String> columnNames = new java.util.ArrayList<>();
+    java.util.List<String> columnTypes = new java.util.ArrayList<>();
+
+    context
+        .getAnalysis()
+        .getOutputDescriptor()
+        .getVisibleFields()
+        .forEach(
+            field -> {
+              columnNames.add(field.getName().orElse("unknown"));
+              columnTypes.add(field.getType().toString());
+            });
+
+    org.apache.tsfile.read.common.block.TsBlockBuilder builder =
+        new org.apache.tsfile.read.common.block.TsBlockBuilder(
+            java.util.Arrays.asList(
+                org.apache.tsfile.enums.TSDataType.TEXT, org.apache.tsfile.enums.TSDataType.TEXT));
+
+    for (int i = 0; i < columnNames.size(); i++) {
+      builder.getTimeColumnBuilder().writeLong(0);
+
+      builder
+          .getColumnBuilder(0)
+          .writeBinary(
+              new org.apache.tsfile.utils.Binary(
+                  columnNames.get(i).getBytes(java.nio.charset.StandardCharsets.UTF_8)));
+      builder
+          .getColumnBuilder(1)
+          .writeBinary(
+              new org.apache.tsfile.utils.Binary(
+                  columnTypes.get(i).getBytes(java.nio.charset.StandardCharsets.UTF_8)));
+
+      builder.declarePosition();
+    }
+
+    return new StatementMemorySource(builder.build(), datasetHeader);
+  }
+
   private List<String> mergeExplainResults(
       Map<NodeRef<Table>, Pair<Integer, List<String>>> cteExplainResults,
       List<String> mainExplainResult) {

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/Analysis.java

@@ -257,6 +257,7 @@ public class Analysis implements IAnalysis {
   private boolean emptyDataSource = false;
 
   private boolean isQuery = false;
+  private boolean isDescribe = false;
 
   // SqlParser is needed during query planning phase for executing uncorrelated scalar subqueries
   // in advance (predicate folding). The planner needs to parse and execute these subqueries
@@ -1552,6 +1553,14 @@ public void setInsert(Insert insert) {
     this.insert = insert;
   }
 
+  public void setDescribe(boolean isDescribe) {
+    this.isDescribe = isDescribe;
+  }
+
+  public boolean isDescribe() {
+    return isDescribe;
+  }
+
   public Insert getInsert() {
     return insert;
   }

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/StatementAnalyzer.java

@@ -80,6 +80,7 @@
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.Delete;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DeleteDevice;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DereferenceExpression;
+import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeQuery;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeTable;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DropColumn;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DropDB;
@@ -850,6 +851,22 @@ protected Scope visitExplain(Explain node, Optional<Scope> context) {
       return visitQuery((Query) node.getStatement(), context);
     }
 
+    @Override
+    protected Scope visitDescribeQuery(DescribeQuery node, Optional<Scope> context) {
+      analysis.setFinishQueryAfterAnalyze(true);
+      Scope scope = visitQuery(node.getQuery(), context);
+
+      RelationType outputDescriptor = analysis.getOutputDescriptor();
+      for (Field field : outputDescriptor.getVisibleFields()) {
+        String name = field.getName().orElse("unknown");
+        String type = field.getType().toString();
+        System.out.println("DESCRIBE_DEBUG: Column=" + name + ", Type=" + type);
+      }
+
+      analysis.setDescribe(true);
+      return scope;
+    }
+
     @Override
     protected Scope visitExplainAnalyze(ExplainAnalyze node, Optional<Scope> context) {
       queryContext.setExplainType(ExplainType.EXPLAIN_ANALYZE);

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/ast/AstVisitor.java

@@ -449,6 +449,10 @@ protected R visitDescribeTable(DescribeTable node, C context) {
     return visitStatement(node, context);
   }
 
+  protected R visitDescribeQuery(DescribeQuery node, C context) {
+    return visitStatement(node, context);
+  }
+
   protected R visitSetProperties(SetProperties node, C context) {
     return visitStatement(node, context);
   }

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/ast/DescribeQuery.java

@@ -0,0 +1,81 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.iotdb.db.queryengine.plan.relational.sql.ast;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.tsfile.utils.RamUsageEstimator;
+
+import java.util.List;
+import java.util.Objects;
+
+import static java.util.Objects.requireNonNull;
+
+public class DescribeQuery extends Statement {
+
+  private static final long INSTANCE_SIZE =
+      RamUsageEstimator.shallowSizeOfInstance(DescribeQuery.class);
+
+  private final Query query;
+
+  public DescribeQuery(NodeLocation location, Query query) {
+    super(requireNonNull(location, "location is null"));
+    this.query = requireNonNull(query, "query is null");
+  }
+
+  public Query getQuery() {
+    return query;
+  }
+
+  @Override
+  public <R, C> R accept(AstVisitor<R, C> visitor, C context) {
+    return visitor.visitDescribeQuery(this, context);
+  }
+
+  @Override
+  public List<Node> getChildren() {
+    return ImmutableList.of(query);
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) return true;
+    if (obj == null || getClass() != obj.getClass()) return false;
+    DescribeQuery that = (DescribeQuery) obj;
+    return Objects.equals(query, that.query);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(query);
+  }
+
+  @Override
+  public String toString() {
+    return "DescribeQuery{" + "query=" + query + '}';
+  }
+
+  @Override
+  public long ramBytesUsed() {
+    long size = INSTANCE_SIZE;
+    size += AstMemoryEstimationHelper.getEstimatedSizeOfNodeLocation(getLocationInternal());
+    size += AstMemoryEstimationHelper.getEstimatedSizeOfAccountableObject(query);
+    return size;
+  }
+}

iotdb-core/relational-grammar/src/main/antlr4/org/apache/iotdb/db/relational/grammar/sql/RelationalSql.g4

@@ -914,6 +914,7 @@ queryStatement
     : query                                                        #statementDefault
     | EXPLAIN query                                                #explain
     | EXPLAIN ANALYZE VERBOSE? query                               #explainAnalyze
+    | DESCRIBE QUERY query                                         #describeQuery
     ;
 
 query