weidong3630 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_r365819703
 
 

 ##########
 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:
   > How about this code:
   > 
   > ```java
   >     if (rel instanceof Aggregate) {
   >         final Aggregate agg = (Aggregate) rel;
   >         final boolean hasNestedAgg = hasNestedAggregations(agg);
   >         if (!dialect.supportsNestedAggregations()
   >             && hasNestedAgg) {
   >           needNew = true;
   >         } else {
   >           if (this.clauses.contains(Clause.GROUP_BY)) {
   >             // Avoids to lose the distinct attribute of inner agg.
   >             if (!hasNestedAgg || Aggregate.isNotGrandTotal(agg)) {
   >               needNew = true;
   >             }
   >           }
   >         }
   >       }
   > ```
   Yeah, it's simpler to my code and it's equivalent to my code.But I think 
that the logic is still a little bit logic confusing.
   

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