[GitHub] [spark] viirya commented on a change in pull request #32303: [SPARK-34382][SQL] Support LATERAL subqueries

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

viirya commented on a change in pull request #32303:
URL: https://github.com/apache/spark/pull/32303#discussion_r619571252



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
##########
@@ -2234,6 +2270,74 @@ class Analyzer(override val catalogManager: CatalogManager)
     }
   }
 
+  /**
+   * This rule resolves lateral joins.
+   */
+  object ResolveLateralJoin extends Rule[LogicalPlan] {
+    import ResolveReferences._
+
+    /**
+     * Build a project list for Project/Aggregate and expand the star if possible by first using
+     * the inner query plan. If failed, use the outer query plan to expand the star and wrap all
+     * expanded attributes in [[OuterReference]]s.
+     */
+    private def expandOuterReference(
+        expressions: Seq[NamedExpression],
+        inner: LogicalPlan,
+        outer: LogicalPlan): Seq[NamedExpression] = {
+
+      def expandInner(star: Star): Seq[NamedExpression] =
+        star.expand(inner, resolver)
+
+      // Leave the star unchanged if the outer plan is unable to resolve the star.
+      // Otherwise wrap the resolved attributes in outer references.
+      def expandOuter(star: Star): Seq[NamedExpression] = {
+        star.expand(outer, resolver).map {
+          case s: Star => s
+          case other => other
+            .transform { case a: Attribute => OuterReference(a) }
+            .asInstanceOf[NamedExpression]
+        }
+      }
+
+      buildExpandedProjectList(
+        buildExpandedProjectList(expressions, inner, expandInner),

Review comment:
       If inner `buildExpandedProjectList` was fully resolved, do we still need run outer `buildExpandedProjectList`?




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