[GitHub] [spark] cloud-fan commented on a diff in pull request #42531: [SPARK-44846][SQL] Pull out complex grouping expressions after remove redundant aggregates

["cloud-fan (via GitHub)" <gi...@apache.org>]

cloud-fan commented on code in PR #42531:
URL: https://github.com/apache/spark/pull/42531#discussion_r1302472237


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAggregates.scala:
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@@ -42,11 +42,12 @@ object RemoveRedundantAggregates extends Rule[LogicalPlan] with AliasHelper {
       )
 
       // We might have introduces non-deterministic grouping expression

Review Comment:
   I have a different idea. I think it's risky to put the new grouping expressions back to the `Aggregate`, as the grouping expression contains things in the SELECT list. This is a long-standing issue and I feel it's better to just create a `Project` below the `Aggregate` to calculate grouping expressions, and other optimizer rules can merge/eliminate this extra `Project` if it only contains `Attributes`.



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