wangyum commented on a change in pull request #31691:
URL: https://github.com/apache/spark/pull/31691#discussion_r594894009
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
##########
@@ -625,6 +626,37 @@ object LimitPushDown extends Rule[LogicalPlan] {
}
}
+/**
+ * Pushes down [[LocalLimit]] beneath WINDOW.
Review comment:
Yes, I plan explain it by SQL,
```scala
/**
* Pushes down [[LocalLimit]] beneath WINDOW. This rule optimizes the
following case:
* {{{
* SELECT *, ROW_NUMBER() OVER(ORDER BY a) AS rn FROM Tab1 LIMIT 5 ==>
* SELECT *, ROW_NUMBER() OVER(ORDER BY a) AS rn FROM (SELECT * FROM Tab1
ORDER BY a LIMIT 5) t
* }}}
*/
```
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