ulysses-you commented on code in PR #37525: URL: https://github.com/apache/spark/pull/37525#discussion_r1091358506
########## sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/AliasAwareOutputExpression.scala: ########## @@ -0,0 +1,116 @@ +/* + * 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.plans + +import scala.collection.mutable + +import org.apache.spark.sql.catalyst.SQLConfHelper +import org.apache.spark.sql.catalyst.expressions.{Alias, Attribute, AttributeSet, Empty2Null, Expression, NamedExpression, SortOrder} +import org.apache.spark.sql.internal.SQLConf + +/** + * A trait that provides functionality to handle aliases in the `outputExpressions`. + */ +trait AliasAwareOutputExpression extends SQLConfHelper { + protected val aliasCandidateLimit = conf.getConf(SQLConf.EXPRESSION_PROJECTION_CANDIDATE_LIMIT) + protected def outputExpressions: Seq[NamedExpression] + /** + * This method can be used to strip expression which does not affect the result, for example: + * strip the expression which is ordering agnostic for output ordering. + */ + protected def strip(expr: Expression): Expression = expr + + // Build an `Expression` -> `Attribute` alias map. + // There can be multiple alias defined for the same expressions but it doesn't make sense to store + // more than `aliasCandidateLimit` attributes for an expression. In those cases the old logic + // handled only the last alias so we need to make sure that we give precedence to that. + // If the `outputExpressions` contain simple attributes we need to add those too to the map. + private lazy val aliasMap = { + val aliases = mutable.Map[Expression, mutable.ArrayBuffer[Attribute]]() + outputExpressions.reverse.foreach { + case a @ Alias(child, _) => + val buffer = aliases.getOrElseUpdate(strip(child.canonicalized), mutable.ArrayBuffer.empty) + if (buffer.size < aliasCandidateLimit) { + buffer += a.toAttribute + } + case _ => + } + outputExpressions.foreach { + case a: Attribute if aliases.contains(a.canonicalized) => + val buffer = aliases(a.canonicalized) + if (buffer.size < aliasCandidateLimit) { + buffer += a + } + case _ => + } + aliases + } + + protected def hasAlias: Boolean = aliasMap.nonEmpty + + /** + * Return a stream of expressions in which the original expression is projected with `aliasMap`. + */ + protected def projectExpression(expr: Expression): Stream[Expression] = { + val outputSet = AttributeSet(outputExpressions.map(_.toAttribute)) + expr.multiTransformDown { + // Mapping with aliases + case e: Expression if aliasMap.contains(e.canonicalized) => + aliasMap(e.canonicalized).toSeq ++ (if (e.containsChild.nonEmpty) Seq(e) else Seq.empty) + + // Prune if we encounter an attribute that we can't map and it is not in output set. + // This prune will go up to the closest `multiTransformDown()` call and returns `Stream.empty` + // there. + case a: Attribute if !outputSet.contains(a) => Seq.empty + } + } +} + +/** + * A trait that handles aliases in the `orderingExpressions` to produce `outputOrdering` that + * satisfies ordering requirements. + */ +trait AliasAwareQueryOutputOrdering[T <: QueryPlan[T]] + extends AliasAwareOutputExpression { self: QueryPlan[T] => + protected def orderingExpressions: Seq[SortOrder] + + override protected def strip(expr: Expression): Expression = expr match { + case e: Empty2Null => strip(e.child) + case _ => expr + } + + override final def outputOrdering: Seq[SortOrder] = { + if (hasAlias) { + orderingExpressions.flatMap { sortOrder => + val orderingSet = mutable.Set.empty[Expression] + val sameOrderings = sortOrder.children.toStream + .flatMap(projectExpression) + .filter(e => orderingSet.add(e.canonicalized)) + .take(aliasCandidateLimit) + if (sameOrderings.nonEmpty) { + Some(sortOrder.copy(child = sameOrderings.head, + sameOrderExpressions = sameOrderings.tail)) + } else { + None + } Review Comment: is it correct ? if `orderingExpressions` is `c1, c2` and aliasMap is `c2 as x`, then the outputOrdering should be `c1, x` or empty rather than `x`. -- This is an automated message from the Apache Git Service. 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