[GitHub] [spark] dongjoon-hyun commented on a change in pull request #27454: [SPARK-28228][SQL] Change the default behavior for name conflict in nested WITH clause

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dongjoon-hyun commented on a change in pull request #27454: [SPARK-28228][SQL] Change the default behavior for name conflict in nested WITH clause
URL: https://github.com/apache/spark/pull/27454#discussion_r376165371
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CTESubstitution.scala
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 @@ -28,10 +29,49 @@ import org.apache.spark.sql.internal.SQLConf.LEGACY_CTE_PRECEDENCE_ENABLED
  */
 object CTESubstitution extends Rule[LogicalPlan] {
   def apply(plan: LogicalPlan): LogicalPlan = {
-    if (SQLConf.get.getConf(LEGACY_CTE_PRECEDENCE_ENABLED)) {
+    val isLegacy = SQLConf.get.getConf(LEGACY_CTE_PRECEDENCE_ENABLED)
+    if (isLegacy.isEmpty) {
+      assertNoNameConflictsInCTE(plan, inTraverse = false)
+      traverseAndSubstituteCTE(plan, inTraverse = false)
+    } else if (isLegacy.get) {
       legacyTraverseAndSubstituteCTE(plan)
     } else {
-      traverseAndSubstituteCTE(plan, false)
+      traverseAndSubstituteCTE(plan, inTraverse = false)
+    }
+  }
+
+  /**
+   * Check the plan to be traversed has naming conflicts in nested CTE or not, traverse through
+   * child, innerChildren and subquery for the current plan.
+   */
+  private def assertNoNameConflictsInCTE(
+      plan: LogicalPlan,
+      inTraverse: Boolean,
+      cteNames: Set[String] = Set.empty): Unit = {
+    plan.foreach {
+      case w @ With(child, relations) =>
+        val newNames = relations.map {
+          case (cteName, _) =>
+            if (cteNames.contains(cteName)) {
+              throw new AnalysisException(s"Name $cteName is conflict in nested CTE. " +
 
 Review comment:
   Ur, `is conflict`? `conflict` is a verb or a noun, isn't it? Shall we revise a little?

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