[GitHub] [calcite] jinxing64 commented on a change in pull request #1606: [CALCITE-3466] Do not drop the "group by" clause of subquery in a select statement with "group by" clause in JDBC adapter.

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jinxing64 commented on a change in pull request #1606: [CALCITE-3466] Do not drop the "group by" clause of subquery in a select statement with "group by" clause in JDBC adapter.
URL: https://github.com/apache/calcite/pull/1606#discussion_r364800580
 
 

 ##########
 File path: core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java
 ##########
 @@ -1224,10 +1224,18 @@ public Builder builder(RelNode rel, Clause... clauses) {
           needNew = true;
         }
       }
-      if (rel instanceof Aggregate
-          && !dialect.supportsNestedAggregations()
-          && hasNestedAggregations((Aggregate) rel)) {
-        needNew = true;
+
+      if (rel instanceof Aggregate) {
+        Aggregate e = (Aggregate) rel;
+        final boolean nestedAgg = hasNestedAggregations(e);
+        if (withGroupBy() && (!e.getGroupSet().toList().isEmpty()
+            || !nestedAgg || !dialect.supportsNestedAggregations())) {
 
 Review comment:
   Shall we have a method as below:
   ```
      // Indicate that whether nested aggregation can be applied.
       public boolean canApplyNestedAggregation(Aggregate agg) {
         return agg.getGroupCount() == 0
             && hasNestedAggregations(agg)
             && dialect.supportsNestedAggregations();
       }
   ```
   So the change here will be much simpler that 
   ```
   ...
         if (rel instanceof Aggregate
             && this.clauses.contains(Clause.GROUP_BY)
             && !canApplyNestedAggregation((Aggregate) rel)) {
           needNew = true;
         }
   ...
   ```

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