Github user sathiyapk commented on a diff in the pull request: https://github.com/apache/spark/pull/19451#discussion_r146603041 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/ReplaceExceptWithFilter.scala --- @@ -0,0 +1,114 @@ +/* + * 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 = plan transform { + case Except(left: Project, right) if isEligible(left, right) => + Project(left.projectList, + Distinct(Filter(Not(transformCondition(left.child, skipProject(right))), left.child))) + + case Except(left, right) if isEligible(left, right) => + Distinct(Filter(Not(transformCondition(left, skipProject(right))), left)) + } + + private def transformCondition(left: LogicalPlan, right: LogicalPlan) = { + val filterCondition = InferFiltersFromConstraints(combineFilters(right) + ).asInstanceOf[Filter].condition + + val attributeNameMap: Map[String, Attribute] = left.output.map(x => (x.name, x)).toMap + val transformedCondition = filterCondition transform { case a : AttributeReference => + attributeNameMap(a.name) + } + + transformedCondition + } + + private def isEligible(left: LogicalPlan, right: LogicalPlan) = (left, right) match { + case (_, right @ (Project(_, _: Filter) | Filter(_, _))) => verifyConditions(left, right) + case _ => false + } + + private def verifyConditions(left: LogicalPlan, right: LogicalPlan) = { + val leftProjectList = projectList(left) + val rightProjectList = projectList(right) + + verifyFilterCondition(skipProject(left)) && verifyFilterCondition(skipProject(right)) && + Project(leftProjectList, nonFilterChild(skipProject(left))).sameResult( + Project(rightProjectList, nonFilterChild(skipProject(right)))) + } + + private def verifyFilterCondition(plan: LogicalPlan) = { --- End diff -- @dilipbiswal well found! the reason for the more rows is in the case 1 of the rule, we put the Filter below the project. As @gatorsmile suggested, we should remove the first case then the Filter will be added above the project, then it will be resolved..
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