maropu commented on a change in pull request #31595:
URL: https://github.com/apache/spark/pull/31595#discussion_r581534668
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
##########
@@ -501,6 +502,46 @@ object RemoveNoopOperators extends Rule[LogicalPlan] {
}
}
+/**
+ * Remove no-op `Union` from the query plan that do not make any modifications.
+ */
+object RemoveNoopUnion extends Rule[LogicalPlan] {
+ /**
+ * This only removes the `Project` that has only attributes or aliased
attributes
+ * from its child.
+ */
+ private def removeAliasOnlyProject(plan: LogicalPlan): LogicalPlan = plan
match {
+ case p @ Project(projectList, child) =>
Review comment:
I thought it was like this:
```
scala> sql("select distinct * from (select id from t1 group by id union
select id as key from t2 group by id)").explain(true)
== Analyzed Logical Plan ==
id: bigint
Distinct
+- Project [id#6L]
+- SubqueryAlias __auto_generated_subquery_name
+- Distinct
+- Union false, false
:- Aggregate [id#6L], [id#6L]
: +- SubqueryAlias spark_catalog.default.t1
: +- Relation[id#6L] parquet
+- Aggregate [id#7L], [id#7L AS key#13L]
+- SubqueryAlias spark_catalog.default.t2
+- Relation[id#7L] parquet
== Optimized Logical Plan ==
Aggregate [id#6L], [id#6L]
+- Aggregate [id#6L], [id#6L]
+- Union false, false
:- Aggregate [id#6L], [id#6L]
: +- Relation[id#6L] parquet
+- Aggregate [id#7L], [id#7L AS key#13L]
+- Relation[id#7L] parquet
```
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