Github user dilipbiswal commented on a diff in the pull request:
https://github.com/apache/spark/pull/17491#discussion_r109191711
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/subquery.scala
---
@@ -498,3 +498,31 @@ object RewriteCorrelatedScalarSubquery extends
Rule[LogicalPlan] {
}
}
}
+
+/**
+ * This rule rewrites a EXISTS predicate sub-queries into an Aggregate
with count.
+ * So it doesn't be converted to a JOIN later.
+ */
+object RewriteEmptyExists extends Rule[LogicalPlan] with PredicateHelper {
+ private def containsAgg(plan: LogicalPlan): Boolean = {
+ plan.collect {
+ case a: Aggregate => a
+ }.nonEmpty
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case Filter(condition, child) =>
+ val (withSubquery, withoutSubquery) =
+
splitConjunctivePredicates(condition).partition(SubqueryExpression.hasInOrExistsSubquery)
+ val newWithSubquery = withSubquery.map(_.transform {
+ case e @ Exists(sub, conditions, exprId) if conditions.isEmpty &&
!containsAgg(sub) =>
--- End diff --
@viirya @nsyca I am still looking at the code. If we do go the route to
turn this into a scalar subquery, would a "limit" help prevent a scan of the
inner table (assuming its very large). So something like "select Count(1) from
(original subquery + limit 1)" ?
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at [email protected] or file a JIRA ticket
with INFRA.
---
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
