jchen5 commented on code in PR #39759:
URL: https://github.com/apache/spark/pull/39759#discussion_r1107634707
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/DecorrelateInnerQuery.scala:
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@@ -254,24 +255,104 @@ object DecorrelateInnerQuery extends PredicateHelper {
/**
* Rewrites a domain join cond so that it can be pushed to the right side of
a
* union/intersect/except operator.
+ *
+ * Example: Take a query like:
+ * select * from t0 join lateral (
+ * select a from t1 where b < t0.x
+ * union all
+ * select b from t2 where c < t0.y)
+ *
+ * We have outer table with attributes [x#1, y#2] and after introducing
DomainJoins the subquery
+ * is a Union where the left side has output [a#3, x#4, y#5] with DomainJoin
[x#4, y#5]
Review Comment:
All the x and y attributes are from t0. They just are different instances of
the attributes - they come from separate joins of the outer table - and have
different expression IDs. Will update the comment to explain that more.
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