dongjoon-hyun commented on a change in pull request #31595:
URL: https://github.com/apache/spark/pull/31595#discussion_r579733849
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -492,12 +492,43 @@ object RemoveRedundantAliases extends Rule[LogicalPlan] {
* Remove no-op operators from the query plan that do not make any
modifications.
*/
object RemoveNoopOperators extends Rule[LogicalPlan] {
+ private def removeAliasOnlyProject(plan: LogicalPlan): LogicalPlan = plan
match {
+ case p @ Project(projectList, child) =>
+ val originalOutputs = projectList.collect {
+ case Alias(a: Attribute, _) => a
+ case a: Attribute => a
+ }
+ if (child.outputSet.nonEmpty && child.outputSet ==
AttributeSet(originalOutputs)) {
+ child
+ } else {
+ p
+ }
+ case _ => plan
+ }
+
def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
// Eliminate no-op Projects
case p @ Project(_, child) if child.sameOutput(p) => child
// Eliminate no-op Window
case w: Window if w.windowExpressions.isEmpty => w.child
+
+ // Eliminate no-op Union
+ case d @ Distinct(u: Union) =>
+ val unionChildren = u.children.map(c => removeAliasOnlyProject(c))
+ if (unionChildren.tail.forall(unionChildren.head.sameResult(_))) {
+ d.withNewChildren(Seq(u.children.head))
+ } else {
+ d
+ }
+
+ case d @ Deduplicate(_, u: Union) =>
Review comment:
If we handle only two cases (`Distinct` and `Deduplicate`), let's say
explicitly `Distinct/Deduplicate` instead of saying `Distinct like operators`.
In general, we use a `whitelist` approach.
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