Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/15238#discussion_r80784941 --- 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 -- All the tail recursion can be converted to a while loop. When I wrote this at that moment, I thought tail recursion was more welcomed than a while loop. : )
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