ulysses-you commented on a change in pull request #35149:
URL: https://github.com/apache/spark/pull/35149#discussion_r781960163
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PropagateEmptyRelation.scala
##########
@@ -59,6 +62,31 @@ abstract class PropagateEmptyRelationBase extends
Rule[LogicalPlan] with CastSup
plan.output.map{ a => Alias(cast(Literal(null), a.dataType),
a.name)(a.exprId) }
protected def commonApplyFunc: PartialFunction[LogicalPlan, LogicalPlan] = {
+ case p: Union if p.children.exists(isEmpty) =>
+ val newChildren = p.children.filterNot(isEmpty)
+ 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 newOutput = outputs.map { case (newAttr, oldAttr) =>
+ if (newAttr.exprId == oldAttr.exprId) {
+ newAttr
+ } else {
+ val newExplicitMetadata =
+ if (oldAttr.metadata != newAttr.metadata)
Some(oldAttr.metadata) else None
+ Alias(newAttr, oldAttr.name)(oldAttr.exprId, explicitMetadata =
newExplicitMetadata)
Review comment:
I checked if the exprId is same, and reuse the original attr if same,
create a new alias if different.
```scala
if (newAttr.exprId == oldAttr.exprId) {
newAttr
} else {
val newExplicitMetadata =
if (oldAttr.metadata != newAttr.metadata) Some(oldAttr.metadata) else
None
Alias(newAttr, oldAttr.name)(oldAttr.exprId, explicitMetadata =
newExplicitMetadata)
}
```
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