[GitHub] [spark] dongjoon-hyun commented on a change in pull request #31113: [SPARK-34061][SQL] DISTINCT the INTERSECT children

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dongjoon-hyun commented on a change in pull request #31113:
URL: https://github.com/apache/spark/pull/31113#discussion_r588905792



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -1663,8 +1663,12 @@ object ReplaceDeduplicateWithAggregate extends Rule[LogicalPlan] {
 /**
  * Replaces logical [[Intersect]] operator with a left-semi [[Join]] operator.
  * {{{
- *   SELECT a1, a2 FROM Tab1 INTERSECT SELECT b1, b2 FROM Tab2
- *   ==>  SELECT DISTINCT a1, a2 FROM Tab1 LEFT SEMI JOIN Tab2 ON a1<=>b1 AND a2<=>b2
+ *   SELECT a1, a2 FROM Tab1 INTERSECT SELECT b1, b2 FROM Tab2 ==>
+ *   SELECT a1, a2 FROM
+ *     (SELECT DISTINCT a1, a2 FROM Tab1)
+ *   LEFT SEMI JOIN
+ *     (SELECT DISTINCT b1, b2 FROM Tab2)

Review comment:
       Do you have any reference from the other DBMSs?




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