cloud-fan commented on code in PR #36530:
URL: https://github.com/apache/spark/pull/36530#discussion_r873517334
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala:
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@@ -139,6 +139,17 @@ object ReorderJoin extends Rule[LogicalPlan] with
PredicateHelper {
* SELECT t1.c1, max(t1.c2) FROM t1 GROUP BY t1.c1
* }}}
*
+ * 3. Remove outer join if:
+ * - For a left outer join with only left-side columns being selected and
the right side join
+ * keys are unique.
+ * - For a right outer join with only right-side columns being selected and
the left side join
+ * keys are unique.
+ *
+ * {{{
+ * SELECT t1.* FROM t1 LEFT JOIN (SELECT DISTINCT c1 as c1 FROM t)t2 ON
t1.c1 = t2.c1 ==>
Review Comment:
```suggestion
* SELECT t1.* FROM t1 LEFT JOIN (SELECT DISTINCT c1 as c1 FROM t) t2 ON
t1.c1 = t2.c1 ==>
```
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