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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