[GitHub] [spark] francis0407 commented on a change in pull request #24344: [SPARK-27440][SQL] Optimize uncorrelated predicate subquery

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francis0407 commented on a change in pull request #24344: [SPARK-27440][SQL] Optimize uncorrelated predicate subquery
URL: https://github.com/apache/spark/pull/24344#discussion_r285871312
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/subquery.scala
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 @@ -93,6 +93,21 @@ object SubqueryExpression {
     }.isDefined
   }
 
+  /**
+   * Returns true when an expression contains a correlated IN or correlated EXISTS and
+   * false otherwise. An IN is non-correlated only if the left values are foldable
+   * and the subquery has no outer references.
+   */
+  def hasCorrelatedInOrExists(e: Expression): Boolean = {
 
 Review comment:
   Moreover, I think `a in (select b from c)` is a `Correlated In` with a `Non-Correlated Subquery`. And we are not going to use a subplan for it. We only need to deal with the `Non-Correlated In`, whose left value should be literal(or foldable) and the right subquery is non-correlated, such as `3 in (select b from c)`.

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