Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/10454#discussion_r48387290
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -858,6 +859,30 @@ 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 {
--- End diff --
If there is a sort, the plan is different. We will have a `Sort` below
`Limit`. Thus, it is not applicable to this rule.
For the full-outer join, I think the result is still correct.
If the nodes below `limit` is deterministic, the result should be
deterministic. Right? Sorry, this part is unclear to me.
Based on my understanding, when we use `limit`, the users will not expect a
deterministic results, unless they use `order by`.
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