cloud-fan commented on code in PR #36530:
URL: https://github.com/apache/spark/pull/36530#discussion_r873346931
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala:
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@@ -211,6 +219,15 @@ object EliminateOuterJoin extends Rule[LogicalPlan] with
PredicateHelper {
if projectList.forall(_.deterministic) &&
p.references.subsetOf(right.outputSet) &&
allDuplicateAgnostic(aggExprs) =>
a.copy(child = p.copy(child = right))
+
+ case p @ Project(_, ExtractEquiJoinKeys(LeftOuter, _, rightKeys, _, _,
left, right, _))
+ if right.distinctKeys.exists(_.subsetOf(ExpressionSet(rightKeys))) &&
+ p.references.subsetOf(left.outputSet) =>
+ p.copy(child = left)
Review Comment:
For a left outer join with only left-side columns being selected, the join
can only change the result if we can find more than one matched row on the
right side. If the right side join keys are unique, apparently we can't find
more than one match. So this optimization LGTM.
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