[CALCITE-7701] Support IGNORE NULLS for FIRST_VALUE/LAST_VALUE window functions in the enumerable convention

core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableWindow.java

@@ -229,7 +229,14 @@ private static void sampleOfTheGeneratedWindowedAggregate() {
       for (int aggIdx = 0; aggIdx < aggregateCalls.size(); aggIdx++) {
         AggregateCall call = aggregateCalls.get(aggIdx);
         if (call.ignoreNulls()) {
-          throw new UnsupportedOperationException("IGNORE NULLS not supported");
+          switch (call.getAggregation().getKind()) {
+          case FIRST_VALUE:
+          case LAST_VALUE:
+            // IGNORE NULLS is implemented for these functions below.
+            break;
+          default:
+            throw new UnsupportedOperationException("IGNORE NULLS not supported");
+          }
         }
         aggs.add(new AggImpState(aggIdx, call, true, implementorTable));
       }
@@ -821,6 +828,10 @@ private void declareAndResetState(final JavaTypeFactory typeFactory,
             @Override public RexWindowExclusion getExclude() {
               return exclusion;
             }
+
+            @Override public boolean ignoreNulls() {
+              return agg.call.ignoreNulls();
+            }
           };
       String aggName = "a" + agg.aggIdx;
       if (CalciteSystemProperty.DEBUG.value()) {

core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java

@@ -35,6 +35,7 @@
 import org.apache.calcite.linq4j.tree.OptimizeShuttle;
 import org.apache.calcite.linq4j.tree.ParameterExpression;
 import org.apache.calcite.linq4j.tree.Primitive;
+import org.apache.calcite.linq4j.tree.Types;
 import org.apache.calcite.linq4j.tree.UnsignedType;
 import org.apache.calcite.rel.type.RelDataType;
 import org.apache.calcite.rel.type.RelDataTypeFactory;
@@ -2489,12 +2490,107 @@
         AggResultContext result) {
       WinAggResultContext winResult = (WinAggResultContext) result;
 
+      final boolean ignoreNulls =
+          info instanceof WinAggContext && ((WinAggContext) info).ignoreNulls();
+      if (ignoreNulls) {
+        return implementResultIgnoreNulls(info, winResult);
+      }
+
       return Expressions.condition(winResult.hasRows(),
           winResult.rowTranslator(
               winResult.computeIndex(Expressions.constant(0), seekType))
               .translate(winResult.rexArguments().get(0), info.returnType()),
           getDefaultValue(info.returnType()));
     }
+
+    /**
+     * Implements FIRST_VALUE / LAST_VALUE with IGNORE NULLS by scanning the
+     * frame (forward for FIRST_VALUE, backward for LAST_VALUE) and returning
+     * the first non-null argument value, or null if all rows in the frame are
+     * null (or the frame is empty).
+     *
+     * <p>Generated code (for FIRST_VALUE; LAST_VALUE scans backward):
+     * <pre>{@code
+     *   BoxType res = null;
+     *   if (hasRows) {
+     *     for (int seekIdx = startIndex; seekIdx <= endIndex; seekIdx++) {
+     *       BoxType seekValue = rowTranslator.translate(arg, boxType);
+     *       if (seekValue != null) {
+     *         res = seekValue;
+     *         break;
+     *       }
+     *     }
+     *   }
+     *   return res;
+     * }</pre>
+     */
+    private Expression implementResultIgnoreNulls(AggContext info,
+        WinAggResultContext winResult) {
+      final Type returnType = info.returnType();
+      final RexNode arg = winResult.rexArguments().get(0);
+
+      // Use a boxed type internally so that a NULL comparison is always valid,
+      // even when the (frame-guaranteed non-empty) return type is a primitive.
+      // The surrounding window implementation converts the result back to the
+      // declared return type.
+      final Type boxType = Types.box(returnType);
+
+      final ParameterExpression res =
+          Expressions.parameter(0, boxType,
+              winResult.currentBlock().newName(
+                  seekType == SeekType.START ? "first_value" : "last_value"));
+      // res = null
+      winResult.currentBlock().add(Expressions.declare(0, res, NULL_EXPR));
+
+      final ParameterExpression idx =
+          Expressions.parameter(int.class,
+              winResult.currentBlock().newName("seekIdx"));
+
+      // Scan direction: FIRST_VALUE walks from start to end, LAST_VALUE walks
+      // from end back to start.
+      final boolean forward = seekType == SeekType.START;
+      final Expression from =
+          forward ? winResult.startIndex() : winResult.endIndex();
+      final Expression to =
+          forward ? winResult.endIndex() : winResult.startIndex();
+      final Expression condition =
+          forward
+              ? Expressions.lessThanOrEqual(idx, to)
+              : Expressions.greaterThanOrEqual(idx, to);
+      final Expression post =
+          forward
+              ? Expressions.postIncrementAssign(idx)
+              : Expressions.postDecrementAssign(idx);
+
+      // Build the loop body:
+      //   BoxType seekValue = rowTranslator.translate(arg, boxType);
+      //   if (seekValue != null) {
+      //     res = seekValue;
+      //     break;
+      //   }
+      final BlockBuilder loopBody = winResult.nestBlock();
+      final Expression value =
+          winResult.rowTranslator(idx).translate(arg, boxType);
+      final ParameterExpression valueVar =
+          Expressions.parameter(0, boxType, loopBody.newName("seekValue"));
+      loopBody.add(Expressions.declare(0, valueVar, value));
+      loopBody.add(
+          Expressions.ifThen(
+              Expressions.notEqual(valueVar, NULL_EXPR),
+              Expressions.block(
+                  Expressions.statement(Expressions.assign(res, valueVar)),
+                  Expressions.break_(null))));
+      winResult.exitBlock();
+      final BlockStatement loopBodyBlock = loopBody.toBlock();
+
+      // Wrap the scan in: if (hasRows) { for (...) { ... } }
+      winResult.currentBlock().add(
+          Expressions.ifThen(winResult.hasRows(),
+              Expressions.for_(
+                  Expressions.declare(0, idx, from),
+                  condition, post, loopBodyBlock)));
+      return res;
+    }
   }
 
   /** Implementor for the {@code FIRST_VALUE} windowed aggregate function. */

core/src/main/java/org/apache/calcite/adapter/enumerable/WinAggContext.java

@@ -26,4 +26,9 @@
 public interface WinAggContext extends AggContext {
   /** The exclude clause of the group of the window function. */
   RexWindowExclusion getExclude();
+
+  /** Whether the window function ignores NULL values (IGNORE NULLS). */
+  default boolean ignoreNulls() {
+    return false;
+  }
 }

core/src/test/resources/sql/winagg.iq

@@ -1323,4 +1323,76 @@ java.sql.SQLException: Error while executing SQL "select first_value(sal) filter
 from emp": FILTER clause is not supported for window function FIRST_VALUE
 !error
 
+# [CALCITE-7701] Support IGNORE NULLS for FIRST_VALUE/LAST_VALUE window functions in the enumerable convention
+# Verified against Oracle
+# FIRST_VALUE with IGNORE NULLS returns the first non-null value in the frame
+# (or NULL if the frame is empty or all values are null).
+select o, v,
+  first_value(v) ignore nulls over (order by o rows 2 preceding) as fv
+from (values (1, 1), (2, cast(null as integer)), (3, 3),
+             (4, cast(null as integer)), (5, cast(null as integer))) as t(o, v);
++---+---+----+
+| O | V | FV |
++---+---+----+
+| 1 | 1 |  1 |
+| 2 |   |  1 |
+| 3 | 3 |  1 |
+| 4 |   |  3 |
+| 5 |   |  3 |
++---+---+----+
+(5 rows)
+
+!ok
+
+# LAST_VALUE with IGNORE NULLS returns the last non-null value in the frame.
+select o, v,
+  last_value(v) ignore nulls over (order by o rows 2 preceding) as lv
+from (values (1, 1), (2, cast(null as integer)), (3, 3),
+             (4, cast(null as integer)), (5, cast(null as integer))) as t(o, v);
++---+---+----+
+| O | V | LV |
++---+---+----+
+| 1 | 1 |  1 |
+| 2 |   |  1 |
+| 3 | 3 |  3 |
+| 4 |   |  3 |
+| 5 |   |  3 |
++---+---+----+
+(5 rows)
+
+!ok
+
+# IGNORE NULLS returns NULL when every row in the frame is null.
+select o, v,
+  first_value(v) ignore nulls
+    over (order by o rows between 1 preceding and 1 preceding) as fv
+from (values (1, cast(null as integer)), (2, cast(null as integer)),
+             (3, 5)) as t(o, v);
++---+---+----+
+| O | V | FV |
++---+---+----+
+| 1 |   |    |
+| 2 |   |    |
+| 3 | 5 |    |
++---+---+----+
+(3 rows)
+
+!ok
+
+# RESPECT NULLS (the default) still returns the boundary value, including NULL.
+select o, v,
+  first_value(v) respect nulls over (order by o rows 2 preceding) as fv,
+  last_value(v) over (order by o rows 2 preceding) as lv
+from (values (1, 1), (2, cast(null as integer)), (3, 3)) as t(o, v);
++---+---+----+----+
+| O | V | FV | LV |
++---+---+----+----+
+| 1 | 1 |  1 |  1 |
+| 2 |   |  1 |    |
+| 3 | 3 |  1 |  3 |
++---+---+----+----+
+(3 rows)
+
+!ok
+
 # End winagg.iq