wangyum commented on a change in pull request #31908:
URL: https://github.com/apache/spark/pull/31908#discussion_r643628381
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
##########
@@ -165,6 +170,23 @@ object EliminateOuterJoin extends Rule[LogicalPlan] with
PredicateHelper {
case f @ Filter(condition, j @ Join(_, _, RightOuter | LeftOuter |
FullOuter, _, _)) =>
val newJoinType = buildNewJoinType(f, j)
if (j.joinType == newJoinType) f else Filter(condition, j.copy(joinType
= newJoinType))
+
+ case a @ Aggregate(_, _, join @ Join(left, _, LeftOuter, _, _))
+ if a.isDistinct && a.references.subsetOf(AttributeSet(left.output)) &&
+ !canPlanAsBroadcastHashJoin(join, conf) =>
Review comment:
The result may be incorrect if always remove the join. For example:
```
0: jdbc:hive2://hdc49-mcc10-01-0510-2005-006-> create table test11.t1 using
parquet as select id % 3 as a, id as b from range(10);
+---------+--+
| Result |
+---------+--+
+---------+--+
No rows selected (1.611 seconds)
0: jdbc:hive2://hdc49-mcc10-01-0510-2005-006-> create table test11.t2 using
parquet as select id % 3 as x, id as y from range(5);
+---------+--+
| Result |
+---------+--+
+---------+--+
No rows selected (1.043 seconds)
0: jdbc:hive2://hdc49-mcc10-01-0510-2005-006-> select t1.a from t1 left join
t2 on a = x;
+----+--+
| a |
+----+--+
| 0 |
| 0 |
| 1 |
| 1 |
| 0 |
| 0 |
| 1 |
| 1 |
| 2 |
| 0 |
| 0 |
| 1 |
| 1 |
| 2 |
| 0 |
| 0 |
| 2 |
+----+--+
17 rows selected (1.409 seconds)
```
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