Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/16255#discussion_r92348878
--- 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
--- End diff --
The problem is: this rule assumes that, if we find an alias-only project,
e.g. alias a#1 to a#2, it's safe to remove this project and replace all a#2
with a#1 in this plan. However, this is not true for complex cases like
https://github.com/apache/spark/pull/16255/files#diff-1ea02a6fab84e938582f7f87cc4d9ea1R2023
.
Let's see if there is a way to fix this problem entirely.
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