[GitHub] [spark] cloud-fan commented on a change in pull request #35214: [SPARK-37915][SQL] Combine unions if there is a project between them

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

cloud-fan commented on a change in pull request #35214:
URL: https://github.com/apache/spark/pull/35214#discussion_r786417032



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -1322,6 +1322,12 @@ object CombineUnions extends Rule[LogicalPlan] {
         case Union(children, byName, allowMissingCol)
             if byName == topByName && allowMissingCol == topAllowMissingCol =>
           stack.pushAll(children.reverse)
+        case Project(projectList, Distinct(u @ Union(children, byName, allowMissingCol)))

Review comment:
       It makes sense to me to accept Project between Unions when combining them. IIRC we did similar things for window optimization.
   
   Shall we make it more general? It seems there are 3 forms of union: Union, Deduplicate + Union, Distinct + Union. Should all these three accept Projects in between?




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