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From gatorsmile <...@git.apache.org>
Subject [GitHub] spark pull request #19451: SPARK-22181 Adds ReplaceExceptWithNotFilter rule
Date Tue, 17 Oct 2017 18:35:42 GMT
Github user gatorsmile commented on a diff in the pull request:

    https://github.com/apache/spark/pull/19451#discussion_r145217301
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/ReplaceExceptWithFilter.scala
---
    @@ -0,0 +1,73 @@
    +/*
    + * 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.{Attribute, AttributeReference, Not}
    +import org.apache.spark.sql.catalyst.plans.logical.{Distinct, Except, Filter, LogicalPlan}
    +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, right) if isEligible(left, right) =>
    +      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)
    +      }
    +
    +      Distinct(Filter(Not(transformedCondition), left))
    +  }
    +
    +  private def isEligible(left: LogicalPlan, right: LogicalPlan): Boolean = (left, right)
match {
    +    case (left, right: Filter) => nonFilterChild(left).sameResult(nonFilterChild(right))
    --- End diff --
    
    This is too restrictive. For example, the children of `EXCEPT` could be `PROJECT`
    
    > SELECT k, v FROM t1 EXCEPT SELECT k, v FROM t1 where v <> 1



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