[GitHub] [spark] cloud-fan commented on pull request #31913: [SPARK-34581][SQL] Don't optimize out grouping expressions from aggregate expressions without aggregate function

[GitBox <gi...@apache.org>]

cloud-fan commented on pull request #31913:
URL: https://github.com/apache/spark/pull/31913#issuecomment-805896134


   Ah this problem is tricky. I think it's error-prone to duplicate the grouping expressions in `Aggregate.groupingExpressions` and `Aggregate.aggregateExpressions`, and assume all the rules will transform them in the same way to keep them the same.
   
   Shall we introduce something like `case class GroupingExprRef(ordinal: Int)` and replace all the grouping expressions with `GroupingExprRef` in `Aggregate.aggregateExpressions` during analysis? Then we don't need to worry about inconsistency anymore.


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