Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/12719#discussion_r62420393
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -617,6 +618,77 @@ object NullPropagation extends Rule[LogicalPlan] {
}
/**
+ * Propagate foldable expressions:
+ * Replace all attributes with aliases of the original foldable
expressions except the followings.
+ * 1) Command and Set(UNION/INTERSECT/EXCEPT): Do not optimize.
--- End diff --
Thank you, @cloud-fan .
* For set queries, they uses **the same AttributeReference** in the global
query and one of subqueries. It causes theoretically incorrect result for
`FoldablePropagation`. We must prevent this.
```
scala> sql("select 1 a union select 2 a").explain
== Physical Plan ==
WholeStageCodegen
: +- TungstenAggregate(key=[a#0], functions=[], output=[a#0])
: +- INPUT
+- Exchange hashpartitioning(a#0, 200), None
+- WholeStageCodegen
: +- TungstenAggregate(key=[a#0], functions=[], output=[a#0])
: +- INPUT
+- Union
:- WholeStageCodegen
: : +- Project [1 AS a#0]
: : +- INPUT
: +- Scan OneRowRelation[]
+- WholeStageCodegen
: +- Project [2 AS a#1]
: +- INPUT
+- Scan OneRowRelation[]
```
* For command queries, it seems some command querys (CTAS) raises
exceptions when they received non-AttributeReference column outputs (here,
aliased literals). Actually, I hope to investigate that as an other issue. It
may need to touch other modules.
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