Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/13884#discussion_r68353553
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -688,6 +688,14 @@ object FoldablePropagation extends Rule[LogicalPlan] {
case c: Command =>
stop = true
c
+ // For outer join, although its output attributes are derived from
its children, they are
+ // actually different attributes: the output of outer join is not
always picked from its
+ // children, but can also be null.
+ // TODO(cloud-fan): It seems more reasonable to use new attributes
as the output attributes
+ // of outer join.
--- End diff --
cc @marmbrus @yhuai @rxin
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