[GitHub] [spark] cloud-fan commented on a change in pull request #34701: [SPARK-37450][SQL] Prune unnecessary fields from Generate under count-only Aggregate

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

cloud-fan commented on a change in pull request #34701:
URL: https://github.com/apache/spark/pull/34701#discussion_r759945029



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -2162,6 +2163,74 @@ object RemoveLiteralFromGroupExpressions extends Rule[LogicalPlan] {
   }
 }
 
+/**
+ * Prunes unnecessary fields from a [[Generate]] if it is under a count aggregation
+ * query.
+ */
+object CountAggregateOptimization extends Rule[LogicalPlan] {

Review comment:
       > also generally empty project cases.
   
   Yea, and not only empty, e.g. `Project(1, child)` can also trigger the optimization, as long as the Project has no references.




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