Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/10577#discussion_r49630582 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala --- @@ -170,17 +173,27 @@ object ExtractFiltersAndInnerJoins extends PredicateHelper { } } + /** * A pattern that collects all adjacent unions and returns their children as a Seq. */ object Unions { def unapply(plan: LogicalPlan): Option[Seq[LogicalPlan]] = plan match { - case u: Union => Some(collectUnionChildren(u)) + case u: Union => Some(collectUnionChildren(ArrayBuffer(u), Seq.empty[LogicalPlan])) case _ => None } - private def collectUnionChildren(plan: LogicalPlan): Seq[LogicalPlan] = plan match { - case Union(l, r) => collectUnionChildren(l) ++ collectUnionChildren(r) - case other => other :: Nil + @tailrec + private def collectUnionChildren( + plan: ArrayBuffer[LogicalPlan], --- End diff -- What I proposed was `Queue`, but the suggestion from @rxin is `ArrayBuffer`. Both are OK for me.
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