Github user marmbrus commented on a diff in the pull request: https://github.com/apache/spark/pull/12590#discussion_r61770196 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala --- @@ -1440,6 +1441,18 @@ object RemoveLiteralFromGroupExpressions extends Rule[LogicalPlan] { } /** + * Removes repetition from group expressions in [[Aggregate]], as they have no effect to the result + * but only makes the grouping key bigger. + */ +object RemoveRepetitionFromGroupExpressions extends Rule[LogicalPlan] { + def apply(plan: LogicalPlan): LogicalPlan = plan transform { + case a @ Aggregate(grouping, _, _) => + val newGrouping = grouping.distinct --- End diff -- This is going to miss cases like `GROUP BY A, a`. I think you want to use an `ExpressionSet` instead of normal `.distinct`
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