Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/16255#discussion_r94361709
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -200,6 +200,8 @@ object RemoveAliasOnlyProject extends Rule[LogicalPlan]
{
case plan: Project if plan eq proj => plan.child
case plan => plan transformExpressions {
case a: Attribute if attrMap.contains(a) => attrMap(a)
+ case b: Alias if attrMap.exists(_._1.exprId == b.exprId)
+ && b.child.isInstanceOf[NamedExpression] => b.child
--- End diff --
How do you reason about this? why we treat `Alias` differently here?
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