peter-toth commented on a change in pull request #29053:
URL: https://github.com/apache/spark/pull/29053#discussion_r453548369
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PropagateEmptyRelation.scala
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@@ -50,8 +50,24 @@ object PropagateEmptyRelation extends Rule[LogicalPlan] with
PredicateHelper wit
override def conf: SQLConf = SQLConf.get
def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
- case p: Union if p.children.forall(isEmptyLocalRelation) =>
- empty(p)
+ case p @ Union(children) if children.exists(isEmptyLocalRelation) =>
+ val newChildren = children.filterNot(isEmptyLocalRelation)
+ if (newChildren.isEmpty) {
+ empty(p)
+ } else {
+ val newPlan = if (newChildren.size > 1) Union(newChildren) else
newChildren.head
+ val outputs = newPlan.output.zip(p.output)
+ // the original Union may produce different output attributes than the
new one so we alias
+ // them if needed
+ if (outputs.forall { case (newAttr, oldAttr) => newAttr.exprId ==
oldAttr.exprId }) {
+ newPlan
+ } else {
+ val outputAliases = outputs.map { case (newAttr, oldAttr) =>
+ Alias(newAttr, oldAttr.name)(oldAttr.exprId)
Review comment:
You are right, we can lose it in some cases. I've fixed in in
https://github.com/apache/spark/pull/29053/commits/cea0a482888daa9ec90d799b0dab2bd643bfa466
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