[GitHub] spark pull request: [SPARK-14830][SQL] Add RemoveRepetitionFromGro...

[marmbrus <gi...@git.apache.org>]

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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