[GitHub] [spark] anchovYu commented on a diff in pull request #38851: [SPARK-41338][SQL] Resolve outer references and normal columns in the same analyzer batch

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

anchovYu commented on code in PR #38851:
URL: https://github.com/apache/spark/pull/38851#discussion_r1036272043


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala:
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@@ -2109,6 +2110,39 @@ class Analyzer(override val catalogManager: CatalogManager)
     }
   }
 
+  /**
+   * Resolves `UnresolvedAttribute` to `OuterReference` if we are resolving subquery plans (when
+   * `AnalysisContext.get.outerPlan` is set). Note that, this rule must be run after
+   * `ResolveReferences` and `ResolveMissingReferences`, as outer reference should be the last
+   * resort during column resolution.
+   */
+  object ResolveOuterReferences extends Rule[LogicalPlan] {
+    override def apply(plan: LogicalPlan): LogicalPlan = {
+      // Only apply this rule if we are resolving subquery plans.
+      if (AnalysisContext.get.outerPlan.isEmpty) return plan
+
+      val preparedPlan = ResolveMissingReferences(ResolveReferences(plan))

Review Comment:
   Is applying these rules once enough? e.g. is it possible that the application of `ResolveMissingReferences` makes more attributes resolvable by `ResolveReferences` and so forth?



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