c21 commented on a change in pull request #31595:
URL: https://github.com/apache/spark/pull/31595#discussion_r580761460
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
##########
@@ -501,6 +502,42 @@ object RemoveNoopOperators extends Rule[LogicalPlan] {
}
}
+/**
+ * Remove no-op `Union` from the query plan that do not make any modifications.
+ */
+object RemoveNoopUnion extends Rule[LogicalPlan] {
+ private def removeAliasOnlyProject(plan: LogicalPlan): LogicalPlan = plan
match {
+ case p @ Project(projectList, child) =>
+ val originalOutputs = projectList.collect {
Review comment:
I feel `collect` is kind of dangerous here, we essentially ignore all
expressions that are not attribute or alias of attribute here. How can it work
correctly?
I am thinking of example query like
```
SELECT DISTINCT k, expr
FROM
(
SELECT k, k + 1 AS expr
FROM test_table
UNION ALL
SELECT k, k + 2 AS expr
FROM test_table
)
```
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