[GitHub] [spark] allisonwang-db commented on a change in pull request #30659: [SPARK-33697][SQL] UnionExec should require column ordering in RemoveRedundantProjects

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allisonwang-db commented on a change in pull request #30659:
URL: https://github.com/apache/spark/pull/30659#discussion_r539001681



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/RemoveRedundantProjects.scala
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@@ -61,15 +63,24 @@ object RemoveRedundantProjects extends Rule[SparkPlan] {
         val keepOrdering = a.aggregateExpressions
           .exists(ae => ae.mode.equals(Final) || ae.mode.equals(PartialMerge))
         a.mapChildren(removeProject(_, keepOrdering))
-      // GenerateExec requires column ordering since it binds input rows directly with its
-      // requiredChildOutput without using child's output schema.
-      case g: GenerateExec => g.mapChildren(removeProject(_, true))
-      // JoinExec ordering requirement will inherit from its parent. If there is no ProjectExec in
-      // its ancestors, JoinExec should require output columns to be ordered.
-      case o => o.mapChildren(removeProject(_, requireOrdering))
+      case p if canPassThrough(p) => p.mapChildren(removeProject(_, requireOrdering))

Review comment:
       Good question. This is because there might be other nodes that require column ordering. An earlier PR also fixed a similar issue for GenerateExec. It is safer to use a whitelist in order to prevent similar issues. Most existing cases are covered (filter, aggregate and join). We can always add more nodes to the whitelist if redundant projects are discovered.




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