Github user davies commented on a diff in the pull request:
https://github.com/apache/spark/pull/12954#discussion_r62388521
--- 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 --
With inner join, the predicate could be pushed down into subquery actually,
but it was not with semi join. So it's not that obvious that which one is
better.
After looking it for a long time, I'm not convinced it's correct ( or the
best way to do it). Could you keep it out of this PR for now?
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