Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/17899#discussion_r124966455 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala --- @@ -610,6 +611,25 @@ object CollapseWindow extends Rule[LogicalPlan] { } /** + * Transpose Adjacent Window Expressions. + * - If the partition spec of the parent Window expression is compatible with the partition spec + * of the child window expression, transpose them. + */ +object TransposeWindow extends Rule[LogicalPlan] { + private def compatibleParititions(ps1 : Seq[Expression], ps2: Seq[Expression]): Boolean = { + ps1.length < ps2.length && ps2.take(ps1.length).permutations.exists(ps1.zip(_).forall { + case (l, r) => l.semanticEquals(r) + }) + } + + def apply(plan: LogicalPlan): LogicalPlan = plan transformUp { + case w1 @ Window(we1, ps1, os1, w2 @ Window(we2, ps2, os2, grandChild)) + if w1.references.intersect(w2.windowOutputSet).isEmpty && compatibleParititions(ps1, ps2) => --- End diff -- No test case covers the condition `w1.references.intersect(w2.windowOutputSet).isEmpty`
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