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https://issues.apache.org/jira/browse/HIVE-18008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16246839#comment-16246839
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Vineet Garg commented on HIVE-18008:
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Should be fixed now
> Add optimization rule to remove gby from right side of left semi-join
> ---------------------------------------------------------------------
>
> Key: HIVE-18008
> URL: https://issues.apache.org/jira/browse/HIVE-18008
> Project: Hive
> Issue Type: Improvement
> Components: Query Planning
> Reporter: Vineet Garg
> Assignee: Vineet Garg
> Attachments: HIVE-18008.1.patch, HIVE-18008.2.patch
>
>
> Group by (on same keys as semi join) as right side of Left semi join is
> unnecessary and could be removed. We see this pattern in subqueries with
> explicit distinct keyword e.g.
> {code:sql}
> explain select * from src b where b.key in (select distinct key from src a
> where a.value = b.value)
> {code}
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