[GitHub] [spark] gengliangwang commented on a diff in pull request #38776: [SPARK-27561][SQL] Support implicit lateral column alias resolution on Project and refactor Analyzer

[GitBox <gi...@apache.org>]

gengliangwang commented on code in PR #38776:
URL: https://github.com/apache/spark/pull/38776#discussion_r1041599676


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveLateralColumnAlias.scala:
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@@ -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 = {

Review Comment:
   This method is quite long...Shall we reduce its size?



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