peter-toth commented on a change in pull request #29053:
URL: https://github.com/apache/spark/pull/29053#discussion_r452690143
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PropagateEmptyRelation.scala
##########
@@ -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) {
Review comment:
Seems to be a good idea, but `sameOutput` uses `semanticEquals` that
fails if an expression is non-deterministic. How about just comparing the
expression ids like this?
```
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)
}
Project(outputAliases, newPlan)
}
}
```
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