[GitHub] [spark] mgaido91 commented on a change in pull request #24442: [SPARK-27547][SQL] fix DataFrame self-join problems

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

mgaido91 commented on a change in pull request #24442: [SPARK-27547][SQL] fix DataFrame self-join problems
URL: https://github.com/apache/spark/pull/24442#discussion_r277701980
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
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 @@ -876,7 +885,30 @@ class Dataset[T] private[sql](
    * @since 2.0.0
    */
   def join(right: Dataset[_]): DataFrame = withPlan {
-    Join(logicalPlan, right.logicalPlan, joinType = Inner, None, JoinHint.NONE)
+    val (joinLeft, joinRight) = prepareJoinPlan(this, right)
+    Join(joinLeft, joinRight, joinType = Inner, None, JoinHint.NONE)
+  }
+
+  // Called by `Dataset#join`, to attach the Dataset id to the logical plan, so that we
+  // can resolve column reference correctly later. See `ResolveDatasetColumnReference`.
+  private def createPlanWithDatasetId(): LogicalPlan = {
+    if (!sparkSession.sessionState.conf.getConf(SQLConf.RESOLVE_DATASET_COLUMN_REFERENCE)) {
+      return logicalPlan
+    }
+
+    // The alias should start with `SubqueryAlias.HIDDEN_ALIAS_PREFIX`, so that `SubqueryAlias` can
 
 Review comment:
   I am not a big fan of using special strings as markers, I'd rather introduce a new attribute to carry on the information.

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