Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/6637#discussion_r31702111
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -696,3 +698,12 @@ object ConvertToLocalRelation extends
Rule[LogicalPlan] {
LocalRelation(projectList.map(_.toAttribute), data.map(projection))
}
}
+
+/**
+ * Replaces logical [[Distinct]] operator with an [[Aggregate]] operator.
+ */
+object ReplaceDistinctWithAggregate extends Rule[LogicalPlan] {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case Distinct(child) => Aggregate(child.output, child.output, child)
--- End diff --
An example in the comment can be useful for understanding:
```
SELECT DISTINCT f1, f2 FROM t ==> SELECT f1, f2 FROM t GROUP BY f1, f2
```
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