peter-toth commented on a change in pull request #29053:
URL: https://github.com/apache/spark/pull/29053#discussion_r452703468
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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 +50,25 @@ 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 newFirstChild = if (newChildren.head eq children.head) {
+ newChildren.head
+ } else {
+ val pl = children.head.output.zip(newChildren.head.output).map {
+ case (oa, na) => Alias(na, oa.name)(oa.exprId)
+ }
+ Project(pl, newChildren.head)
+ }
Review comment:
It looks like it is idempotent and doesn't do costly things just a
simple bottom-up traversal on nodes and one expression traversal per node.
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