Github user gengliangwang commented on a diff in the pull request: https://github.com/apache/spark/pull/19451#discussion_r143808170 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala --- @@ -1242,6 +1243,53 @@ object ReplaceIntersectWithSemiJoin extends Rule[LogicalPlan] { } /** + * If one or both of the datasets in the logical [[Except]] operator are purely transformed using + * [[Filter]], this rule will replace logical [[Except]] operator with a [[Filter]] operator by + * flipping the filter condition of the right child. + * {{{ + * SELECT a1, a2 FROM Tab1 WHERE a2 = 12 EXCEPT SELECT a1, a2 FROM Tab1 WHERE a1 = 5 + * ==> SELECT a1, a2 FROM Tab1 WHERE a2 = 12 AND a1 <> 5 + * }}} + * + * Note: + * 1. We should combine all the [[Filter]] of the right node before flipping it using NOT operator. + */ +object ReplaceExceptWithNotFilter extends Rule[LogicalPlan] { + + implicit def nodeToFilter(node: LogicalPlan): Filter = node.asInstanceOf[Filter] + + def apply(plan: LogicalPlan): LogicalPlan = plan transform { + case Except(left, right) if isEligible(left, right) => + Distinct( + Filter(Not(replaceAttributesIn(combineFilters(right).condition, left)), left) + ) + } + + def isEligible(left: LogicalPlan, right: LogicalPlan): Boolean = (left, right) match { + case (left: Filter, right: Filter) => parent(left).sameResult(parent(right)) + case (left, right: Filter) => left.sameResult(parent(right)) + case _ => false + } + + def parent(plan: LogicalPlan): LogicalPlan = plan match { + case x @ Filter(_, child) => parent(child) + case x => x + } + + def combineFilters(plan: LogicalPlan): LogicalPlan = CombineFilters(plan) match { --- End diff -- I think `CombineFilters(plan)` can finish in one pass.
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