Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/10454#discussion_r48378249
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -858,6 +859,26 @@ object PushPredicateThroughJoin extends
Rule[LogicalPlan] with PredicateHelper {
}
/**
+ * Push [[Limit]] operators through [[Join]] operators, iff the join type
is outer joins.
+ * Adding extra [[Limit]] operators on top of the outer-side
child/children.
+ */
+object PushLimitThroughOuterJoin extends Rule[LogicalPlan] with
PredicateHelper {
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case f @ Limit(expr, Join(left, right, joinType, joinCondition)) =>
+ joinType match {
+ case RightOuter =>
+ Limit(expr, Join(left, Limit(expr, right), joinType,
joinCondition))
+ case LeftOuter =>
+ Limit(expr, Join(Limit(expr, left), right, joinType,
joinCondition))
+ case FullOuter =>
+ Limit(expr, Join(Limit(expr, left), Limit(expr, right),
joinType, joinCondition))
+ case _ => f // DO Nothing for the other join types
+ }
+ }
+}
--- End diff --
You are right, but, after this rule, there exists another rule
`CombineLimits`, which can combine the extra limits. I think we should still
fix it anyway. Thanks!
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