cloud-fan commented on code in PR #36417:
URL: https://github.com/apache/spark/pull/36417#discussion_r866652724
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala:
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@@ -750,6 +749,11 @@ object LimitPushDown extends Rule[LogicalPlan] {
Limit(le, Project(a.aggregateExpressions, LocalLimit(le, a.child)))
case Limit(le @ IntegerLiteral(1), p @ Project(_, a: Aggregate)) if
a.groupOnly =>
Limit(le, p.copy(child = Project(a.aggregateExpressions, LocalLimit(le,
a.child))))
+ // Merge offset value and limit value into LocalLimit and pushes down
LocalLimit through Offset.
+ case LocalLimit(le, Offset(oe @ IntegerLiteral(offset), grandChild)) if
offset > 0 =>
+ Offset(oe, LocalLimit(Add(le, oe), grandChild))
+ // Eliminate Offset if offset value equals 0.
+ case Offset(IntegerLiteral(0), child) => child
Review Comment:
We can add a new rule `EliminateOffsets` for this. And there is one more
idea: if `child.maxRows < offset`, then we can simply turn the query into a
empty local relation.
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