Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/16255#discussion_r92349611
--- 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 --
a naive way to do this is, make sure we only replace attributes in the
ancestor nodes of the alias-only project:
```
plan transform {
case plan: Project if plan eq proj => plan.child
case plan if plan.collect { case p if p eq project }.nonEmpty => // do
the replace
}
```
It's very inefficient, maybe we can improve `TreeNode` to maintain the
parent-child relationship between nodes.
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