sigmod commented on code in PR #36909:
URL: https://github.com/apache/spark/pull/36909#discussion_r904002034
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala:
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@@ -753,6 +753,9 @@ object LimitPushDown extends Rule[LogicalPlan] {
// Merge offset value and limit value into LocalLimit and pushes down
LocalLimit through Offset.
case LocalLimit(le, Offset(oe, grandChild)) =>
Offset(oe, LocalLimit(Add(le, oe), grandChild))
+ // Push down local limit 1 if join type is LeftSemiOrAnti and join
condition is empty.
+ case j @ Join(_, right, LeftSemiOrAnti(_), None, _) if
!right.maxRows.exists(_ <= 1) =>
Review Comment:
> when right.maxRows > 0. It can not guarantee the result must not be empty.
- For left semi with empty condition, it doesn't matter? Non empty `right`
means all `left` rows are join output rows?
- For left anti with empty condition, it doesn't matter neither? Non empty
`right` means all `left` rows are killed and join doesn't output any row?
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