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https://issues.apache.org/jira/browse/HIVE-17767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16237779#comment-16237779
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Ashutosh Chauhan commented on HIVE-17767:
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Looks like few tests need update.
> Rewrite correlated EXISTS/IN subqueries into LEFT SEMI JOIN
> -----------------------------------------------------------
>
> Key: HIVE-17767
> URL: https://issues.apache.org/jira/browse/HIVE-17767
> Project: Hive
> Issue Type: Improvement
> Components: Query Planning
> Reporter: Vineet Garg
> Assignee: Vineet Garg
> Priority: Major
> Attachments: HIVE-17767.1.patch, HIVE-17767.2.patch,
> HIVE-17767.3.patch, HIVE-17767.4.patch
>
>
> Currently such queries are written into group by + inner join with value
> generator and is inefficient. Value generator consists of join with outer
> query to fetch all correlated values. This value generator could be
> completely eliminated if such queries are instead rewritten into LEFT SEMI
> JOIN.
> Note that to do this first hive need to support LEFT SEMI JOIN with non-equi
> condition (HIVE-17766).
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