Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/19451#discussion_r147507850 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/ReplaceExceptWithFilter.scala --- @@ -0,0 +1,104 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.spark.sql.catalyst.optimizer + +import scala.annotation.tailrec + +import org.apache.spark.sql.catalyst.expressions._ +import org.apache.spark.sql.catalyst.plans.logical._ +import org.apache.spark.sql.catalyst.rules.Rule + + +/** + * 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 DISTINCT a1, a2 FROM Tab1 WHERE a2 = 12 AND (a1 is null OR a1 <> 5) + * }}} + * + * Note: + * Before flipping the filter condition of the right node, we should: + * 1. Combine all it's [[Filter]]. + * 2. Apply InferFiltersFromConstraints rule (to support NULL values of the condition). + */ +object ReplaceExceptWithFilter extends Rule[LogicalPlan] { + + def apply(plan: LogicalPlan): LogicalPlan = { + if (!plan.conf.replaceExceptWithFilter) { + return plan + } + + plan.transform { + case Except(left, right) if isEligible(left, right) => + Distinct(Filter(Not(transformCondition(left, skipProject(right))), left)) + } + } + + private def transformCondition(left: LogicalPlan, right: LogicalPlan): Expression = { + val filterCondition = InferFiltersFromConstraints(combineFilters(right) + ).asInstanceOf[Filter].condition --- End diff -- ```Scala val filterCondition = InferFiltersFromConstraints(combineFilters(right)).asInstanceOf[Filter].condition ```
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