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_r285879099
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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:
Push down the LHS of IN into the subquery is the first step. We can also use
a specific aggregation to reduce the result set to an acceptable size.
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