wangyum commented on a change in pull request #35214:
URL: https://github.com/apache/spark/pull/35214#discussion_r787589160
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
##########
@@ -1322,6 +1322,12 @@ object CombineUnions extends Rule[LogicalPlan] {
case Union(children, byName, allowMissingCol)
if byName == topByName && allowMissingCol == topAllowMissingCol =>
stack.pushAll(children.reverse)
+ case Project(projectList, Distinct(u @ Union(children, byName,
allowMissingCol)))
+ if projectList.forall(_.deterministic) && children.nonEmpty &&
+ flattenDistinct && byName == topByName && allowMissingCol ==
topAllowMissingCol =>
+ val newChildren =
PushProjectionThroughUnion.pushProjectionThroughUnion(projectList, u)
+ .map(CollapseProject(_))
Review comment:
We will put all children to stack and use it later. For example, if we
do not collapse projects. we can not [extract union‘s
children](https://github.com/apache/spark/blob/ab18cc8a7d3df476f045f84bae4ff121eacc91b9/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala#L1326-L1343):
```
Project [cast(id#34 as decimal(22,5)) AS id#36]
+- Project [cast(id#32 as decimal(21,4)) AS id#34]
+- Distinct
+- Union false, false
:- Project [cast(id#30 as decimal(20,3)) AS id#32]
: +- Distinct
: +- Union false, false
: :- Project [cast(id#25 as decimal(19,2)) AS id#30]
: : +- Relation default.t1[id#25] parquet
: +- Project [cast(id#26 as decimal(19,2)) AS id#31]
: +- Relation default.t2[id#26] parquet
+- Project [cast(id#27 as decimal(20,3)) AS id#33]
+- Relation default.t3[id#27] parquet
```
And later we will do `ReplaceDistinctWithAggregate` and then `CombineUnions`
can not combine any unions.
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