maropu commented on a change in pull request #31045:
URL: https://github.com/apache/spark/pull/31045#discussion_r552255103
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -1612,9 +1612,12 @@ object ConvertToLocalRelation extends Rule[LogicalPlan] {
* {{{
* SELECT DISTINCT f1, f2 FROM t ==> SELECT f1, f2 FROM t GROUP BY f1, f2
* }}}
+ *
+ * The [[Distinct]] can be ignored if it is the right child of a left semi or
anti join.
*/
object ReplaceDistinctWithAggregate extends Rule[LogicalPlan] {
- def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transformDown {
+ case j @ Join(_, Distinct(right), LeftSemiOrAnti(_), _, _) => j.copy(right
= right)
Review comment:
Just out of curiosity, this rule can always make performance better? For
example, how about the case where a right table has too many duplicates?
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