cloud-fan commented on code in PR #38776: URL: https://github.com/apache/spark/pull/38776#discussion_r1040868659
########## sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveLateralColumnAlias.scala: ########## @@ -0,0 +1,222 @@ +/* + * 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.analysis + +import org.apache.spark.sql.catalyst.expressions.{Alias, LateralColumnAliasReference, NamedExpression, OuterReference} +import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, OneRowRelation, Project} +import org.apache.spark.sql.catalyst.rules.{Rule, UnknownRuleId} +import org.apache.spark.sql.catalyst.trees.TreePattern.{LATERAL_COLUMN_ALIAS_REFERENCE, OUTER_REFERENCE, UNRESOLVED_ATTRIBUTE} +import org.apache.spark.sql.catalyst.util.CaseInsensitiveMap +import org.apache.spark.sql.errors.QueryCompilationErrors +import org.apache.spark.sql.internal.SQLConf + +/** + * Resolve lateral column alias, which references the alias defined previously in the SELECT list. + * Plan-wise it handles two types of operators: Project and Aggregate. + * - in Project, pushing down the referenced lateral alias into a newly created Project, resolve + * the attributes referencing these aliases + * - in Aggregate TODO. + * + * The whole process is generally divided into two phases: + * 1) recognize resolved lateral alias, wrap the attributes referencing them with + * [[LateralColumnAliasReference]] + * 2) when the whole operator is resolved, unwrap [[LateralColumnAliasReference]]. + * For Project, it further resolves the attributes and push down the referenced lateral aliases. + * For Aggregate, TODO + * + * Example for Project: + * Before rewrite: + * Project [age AS a, 'a + 1] + * +- Child + * + * After phase 1: + * Project [age AS a, lateralalias(a) + 1] + * +- Child + * + * After phase 2: + * Project [a, a + 1] + * +- Project [child output, age AS a] + * +- Child + * + * Example for Aggregate TODO + * + * + * The name resolution priority: + * local table column > local lateral column alias > outer reference + * + * Because lateral column alias has higher resolution priority than outer reference, it will try + * to resolve an [[OuterReference]] using lateral column alias in phase 1, similar as an + * [[UnresolvedAttribute]]. If success, it strips [[OuterReference]] and also wraps it with + * [[LateralColumnAliasReference]]. + */ +// TODO revisit resolving order: top down, or bottom up +object ResolveLateralColumnAlias extends Rule[LogicalPlan] { + def resolver: Resolver = conf.resolver + + private case class AliasEntry(alias: Alias, index: Int) + private def insertIntoAliasMap( + a: Alias, + idx: Int, + aliasMap: CaseInsensitiveMap[Seq[AliasEntry]]): CaseInsensitiveMap[Seq[AliasEntry]] = { + val prevAliases = aliasMap.getOrElse(a.name, Seq.empty[AliasEntry]) + aliasMap + (a.name -> (prevAliases :+ AliasEntry(a, idx))) + } + + /** + * Use the given the lateral alias candidate to resolve the name parts. + * @return The resolved attribute if succeeds. None if fails to resolve. + */ + private def resolveByLateralAlias( + nameParts: Seq[String], lateralAlias: Alias): Option[NamedExpression] = { + val resolvedAttr = Analyzer.resolveExpressionByPlanOutput( + expr = UnresolvedAttribute(nameParts), + plan = Project(Seq(lateralAlias), OneRowRelation()), + resolver = resolver, + throws = false + ).asInstanceOf[NamedExpression] + if (resolvedAttr.resolved) Some(resolvedAttr) else None + } + + private def rewriteLateralColumnAlias(plan: LogicalPlan): LogicalPlan = { + // phase 1: wrap + val rewrittenPlan = plan.resolveOperatorsUpWithPruning( + _.containsAnyPattern(UNRESOLVED_ATTRIBUTE, OUTER_REFERENCE), ruleId) { + case p @ Project(projectList, child) if p.childrenResolved + && !Analyzer.containsStar(projectList) + && projectList.exists(_.containsAnyPattern(UNRESOLVED_ATTRIBUTE, OUTER_REFERENCE)) => + + var aliasMap = CaseInsensitiveMap(Map[String, Seq[AliasEntry]]()) + def wrapLCAReference(e: NamedExpression): NamedExpression = { + e.transformWithPruning(_.containsAnyPattern(UNRESOLVED_ATTRIBUTE, OUTER_REFERENCE)) { + case o: OuterReference + if aliasMap.contains(o.nameParts.map(_.head).getOrElse(o.name)) => + val nameParts = o.nameParts.getOrElse(Seq(o.name)) + val aliases = aliasMap.get(nameParts.head).get + aliases.size match { + case n if n > 1 => + throw QueryCompilationErrors.ambiguousLateralColumnAlias(nameParts, n) + case n if n == 1 && aliases.head.alias.resolved => + // Only resolved alias can be the lateral column alias + resolveByLateralAlias(nameParts, aliases.head.alias) + .map(LateralColumnAliasReference(_, nameParts)) + .getOrElse(o) + case _ => o + } + case u: UnresolvedAttribute if aliasMap.contains(u.nameParts.head) && + Analyzer.resolveExpressionByPlanChildren(u, p, resolver) + .isInstanceOf[UnresolvedAttribute] => + val aliases = aliasMap.get(u.nameParts.head).get + aliases.size match { + case n if n > 1 => + throw QueryCompilationErrors.ambiguousLateralColumnAlias(u.name, n) + case n if n == 1 && aliases.head.alias.resolved => + // Only resolved alias can be the lateral column alias + resolveByLateralAlias(u.nameParts, aliases.head.alias) + .map(LateralColumnAliasReference(_, u.nameParts)) + .getOrElse(u) + case _ => u + } + }.asInstanceOf[NamedExpression] + } + val newProjectList = projectList.zipWithIndex.map { + case (a: Alias, idx) => + val lcaWrapped = wrapLCAReference(a).asInstanceOf[Alias] + // Insert the LCA-resolved alias instead of the unresolved one into map. If it is + // resolved, it can be referenced as LCA by later expressions (chaining). + // Unresolved Alias is also added to the map to perform ambiguous name check, but only + // resolved alias can be LCA + aliasMap = insertIntoAliasMap(lcaWrapped, idx, aliasMap) + lcaWrapped + case (e, _) => + wrapLCAReference(e) + } + p.copy(projectList = newProjectList) + } + + // phase 2: unwrap + rewrittenPlan.resolveOperatorsUpWithPruning( + _.containsPattern(LATERAL_COLUMN_ALIAS_REFERENCE), UnknownRuleId) { + case p @ Project(projectList, child) if p.resolved + && projectList.exists(_.containsPattern(LATERAL_COLUMN_ALIAS_REFERENCE)) => + // build the map again in case the project list changes and index goes off + // TODO one risk: is there any rule that strips off /add the Alias? that the LCA is resolved + // in the beginning, but when it comes to push down, it really can't find the matching one? Review Comment: I don't think we will strip top-level alias. But if other rules split `Project`, then an alias may become an attribute in the upper `Project`. Fortunately I'm not aware of such rules. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
