xiedeyantu commented on code in PR #4495:
URL: https://github.com/apache/calcite/pull/4495#discussion_r2264166343


##########
core/src/main/java/org/apache/calcite/tools/RelBuilder.java:
##########
@@ -2819,28 +2819,56 @@ private RelBuilder aggregate_(ImmutableBitSet groupSet,
    * GROUP_ID returns wrong result</a> and
    * <a 
href="https://issues.apache.org/jira/browse/CALCITE-4748";>[CALCITE-4748]
    * If there are duplicate GROUPING SETS, Calcite should return duplicate
-   * rows</a>.
+   * rows</a> and
+   * <a 
href="https://issues.apache.org/jira/browse/CALCITE-7126";>[CALCITE-7126]
+   * The calculation result of grouping function is wrong</a>.
    */
   private RelBuilder rewriteAggregateWithDuplicateGroupSets(
       ImmutableBitSet groupSet,
       ImmutableSortedMultiset<ImmutableBitSet> groupSets,
       List<AggCallPlus> aggregateCalls) {
+    List<AggregateCall> calls =
+        aggregateCalls.stream()
+            .map(AggCallPlus::aggregateCall)
+            .collect(Collectors.toList());
+    return rewriteAggregateWithDuplicateGroupSetsImpl(groupSet, groupSets, 
calls);
+  }
+
+  private RelBuilder rewriteAggregateWithDuplicateGroupSetsImpl(
+      ImmutableBitSet groupSet,
+      ImmutableSortedMultiset<ImmutableBitSet> groupSets,
+      List<AggregateCall> aggregateCalls) {
+    final int groupCount = groupSet.cardinality();
+    // No need to handle the case without GROUP BY in aggregate.
+    if (groupCount > 0) {
+      aggregateCalls = aggregateCalls.stream()
+          .map(c -> c.withAllowChangeNullable(false))
+          .collect(Collectors.toList());
+    }
+
     final List<String> fieldNamesIfNoRewrite =
-        Aggregate.deriveRowType(getTypeFactory(), peek().getRowType(), false,
-            groupSet, groupSets.asList(),
-            aggregateCalls.stream().map(AggCallPlus::aggregateCall)
-                .collect(toImmutableList())).getFieldNames();
-
-    // If n duplicates exist for a particular grouping, the {@code GROUP_ID()}
-    // function produces values in the range 0 to n-1. For each value,
-    // we need to figure out the corresponding group sets.
-    //
-    // For example, "... GROUPING SETS (a, a, b, c, c, c, c)"
-    // (i) The max value of the GROUP_ID() function returns is 3
-    // (ii) GROUPING SETS (a, b, c) produces value 0,
-    //      GROUPING SETS (a, c) produces value 1,
-    //      GROUPING SETS (c) produces value 2
-    //      GROUPING SETS (c) produces value 3
+        Aggregate.deriveRowType(getTypeFactory(), peek().getRowType(),

Review Comment:
   I also think this is a very good comment. I have kept the first two 
versions, but the last version was accidentally lost. I will make up for it.



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