Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/11599#discussion_r55482347
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -380,6 +380,9 @@ object ColumnPruning extends Rule[LogicalPlan] {
p
}
+ // Eliminate the Projects with empty projectList
+ case p @ Project(projectList, child) if projectList.isEmpty => child
--- End diff --
Let me respond the original question by @cloud-fan
We will not see an empty Project, if the child has more than one columns.
The empty Project only happens after columnPruning. I am fine, if we want to
add an extra rule for eliminating Project only.
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