anchovYu commented on code in PR #38776:
URL: https://github.com/apache/spark/pull/38776#discussion_r1041325612


##########
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?
+        //  Restore back to UnresolvedAttribute.
+        //  Also, when resolving from bottom up should I worry about cases 
like:
+        //  Project [b AS c, c + 1 AS d]
+        //  +- Project [1 AS a, a AS b]
+        //  b AS c is resolved, even b refers to an alias contains the lateral 
alias?
+        var aliasMap = CaseInsensitiveMap(Map[String, Seq[AliasEntry]]())
+        val referencedAliases = collection.mutable.Set.empty[AliasEntry]
+        def unwrapLCAReference(e: NamedExpression): NamedExpression = {
+          
e.transformWithPruning(_.containsAnyPattern(LATERAL_COLUMN_ALIAS_REFERENCE)) {
+            case lcaRef: LateralColumnAliasReference if 
aliasMap.contains(lcaRef.nameParts.head) =>
+              val aliasEntry = aliasMap.get(lcaRef.nameParts.head).get.head
+              if 
(!aliasEntry.alias.containsPattern(LATERAL_COLUMN_ALIAS_REFERENCE)) {
+                // If there is no chaining, push down the alias and resolve 
the attribute by
+                // constructing a dummy plan
+                referencedAliases += aliasEntry
+                // Implementation notes (to-delete):
+                // this is a design decision whether to restore the 
UnresolvedAttribute, or
+                // directly resolve by constructing a plan and using 
resolveExpressionByPlanChildren
+                resolveByLateralAlias(lcaRef.nameParts, 
aliasEntry.alias).getOrElse(lcaRef)

Review Comment:
   I think it is safe to resolve it one more time, in case the alias or the 
field changes or is reconstructed (different exprId).



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