Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/12306#discussion_r60008557
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala
---
@@ -110,6 +110,31 @@ trait CheckAnalysis {
s"filter expression '${f.condition.sql}' " +
s"of type ${f.condition.dataType.simpleString} is not a
boolean.")
+ case f @ Filter(condition, child) =>
+ // Make sure no correlated predicate is in an OUTER join,
because this could change the
+ // semantics of the join.
+ lazy val attributes: Set[Expression] = child.output.toSet
+ def checkCorrelatedPredicates(p: PredicateSubquery): Unit =
p.query.foreach {
+ case j @ Join(left, right, jt, _) if jt != Inner =>
+ j.transformAllExpressions {
+ case e if attributes.contains(e) =>
+ failAnalysis(s"Accessing outer query column is not
allowed in outer joins: $e")
--- End diff --
`l.id` shouldn't be part of the join condition either. It would not make
any difference; the join could produce more null values and that is all. There
should be WHERE after the join, e.g.:
SELECT *
FROM l
WHERE EXISTS(SELECT *
FROM r
LEFT JOIN (SELECT * FROM s) t
ON t.id = r.id
WHERE t.id = l.id)
It could be usefull the pull out correlated predicates from an inner join
though (I have never seen this in the wild though).
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