Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/12954#discussion_r62382186
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -1645,3 +1646,30 @@ object RewriteCorrelatedScalarSubquery extends
Rule[LogicalPlan] {
}
}
}
+
+/**
+ * Rewrite [[Filter]] plans that contain correlated [[ScalarSubquery]]
expressions. When these
+ * correlated [[ScalarSubquery]] expressions are wrapped in a some
Predicate expression, we rewrite
+ * them into [[PredicateSubquery]] expressions.
+ */
+object RewriteScalarSubqueriesInFilter extends Rule[LogicalPlan] {
--- End diff --
It is not nessecary for this fix. It is left over from the initial attempt.
I do think it adds value, since it allows us to use queries which might return
multiple values for one key.
We do have a rule that promotes and outer join into an inner join, but we
do not have one that turns a outer/inner join into a semi join.
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