Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/15238#discussion_r80753108
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
---
@@ -191,25 +191,34 @@ object ExtractFiltersAndInnerJoins extends
PredicateHelper {
/**
* A pattern that collects all adjacent unions and returns their children
as a Seq.
+ * If the top union is wrapped in a [[Distinct]], then the [[Distinct]] in
the adjacent unions, if
+ * any, will be eliminated.
*/
object Unions {
- def unapply(plan: LogicalPlan): Option[Seq[LogicalPlan]] = plan match {
- case u: Union => Some(collectUnionChildren(mutable.Stack(u),
Seq.empty[LogicalPlan]))
+ def unapply(plan: LogicalPlan): Option[(Seq[LogicalPlan], Boolean)] =
plan match {
+ case u: Union =>
+ Some(collectUnionChildren(mutable.Stack(u), Seq.empty[LogicalPlan],
false), false)
+ case Distinct(u: Union) =>
+ Some(collectUnionChildren(mutable.Stack(u), Seq.empty[LogicalPlan],
true), true)
case _ => None
}
// Doing a depth-first tree traversal to combine all the union children.
@tailrec
private def collectUnionChildren(
plans: mutable.Stack[LogicalPlan],
- children: Seq[LogicalPlan]): Seq[LogicalPlan] = {
+ children: Seq[LogicalPlan],
+ dedupDistinct: Boolean): Seq[LogicalPlan] = {
--- End diff --
Why is this method so complicated? It seems that we can do without the
stack. A stack only makes sense if you do not want use recursion (you can use a
while loop instead). This comment has nothing to do with this PR, but with the
code as it was to begin with. Could you fix it anyway?
cc @gatorsmile as well
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