cloud-fan commented on code in PR #37334:
URL: https://github.com/apache/spark/pull/37334#discussion_r934142316
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala:
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@@ -559,6 +561,17 @@ object RemoveRedundantAliases extends Rule[LogicalPlan] {
})
Join(newLeft, newRight, joinType, newCondition, hint)
+ case _: Union =>
Review Comment:
Looking at the code again, I think for Union, we can remove aliases as long
as it does not introduce conflicting attr IDs. For example, `Union(Project(a#1,
a#1 as a#2, ...), ...)`, we can't remove the alias. But for `Union(Project(a#1
as a#2, ...), ...)`, we can.
If this was when we first add this rule, I won't bother to have unnecessary
alias in the first child of Union. But this is a bug fix, and I think don't
lose any optimization we had before is safer.
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