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https://issues.apache.org/jira/browse/SPARK-27229?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16798681#comment-16798681
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Hyukjin Kwon commented on SPARK-27229:
--------------------------------------
Please avoid to set Critical+ which is usually reserved for committers.
> GroupBy Placement in Intersect Distinct
> ---------------------------------------
>
> Key: SPARK-27229
> URL: https://issues.apache.org/jira/browse/SPARK-27229
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Song Jun
> Priority: Major
>
> Intersect operator will be replace by Left Semi Join in Optimizer.
> for example:
> 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
> if Tabe1 and Tab2 are too large, the join will be very slow, we can reduce
> the table data before
> Join by place groupby operator under join, that is
> ==>
> SELECT a1, a2 FROM
> (SELECT a1,a2 FROM Tab1 GROUP BY a1,a2) X
> LEFT SEMI JOIN
> (SELECT b1,b2 FROM Tab2 GROUP BY b1,b2) Y
> ON X.a1<=>Y.b1 AND X.a2<=>Y.b2
> then we can have smaller table data when execute join, because group by has
> cut lots of
> data.
>
> A pr will be submit soon
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