ulysses-you commented on a change in pull request #27048: [SPARK-30386][SQL]
Pushdown limit to outer join through projects
URL: https://github.com/apache/spark/pull/27048#discussion_r362376835
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -495,6 +495,18 @@ object LimitPushDown extends Rule[LogicalPlan] {
case _ => join
}
LocalLimit(exp, newJoin)
+ // Pushdown limit to outer join through projects if projects are
deterministic.
+ case l @ LocalLimit(exp, proj @ Project(projs, join @ Join(left, right,
joinType, _, _))) =>
Review comment:
It pushed. When execute `explain extended select c from test union all
select c from test limit 1`, the optimized plan is
```
GlobalLimit 1
+- LocalLimit 1
+- Union
:- LocalLimit 1
: +- Relation[c#50] parquet
+- LocalLimit 1
+- Relation[c#50] parquet
```
The difference is another optimizer `PushProjectionThroughUnion` has pushed
down `Project`.
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