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https://issues.apache.org/jira/browse/HIVE-15839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15864563#comment-15864563
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Wei Zheng commented on HIVE-15839:
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+1
> Don't force cardinality check if only WHEN NOT MATCHED is specified
> -------------------------------------------------------------------
>
> Key: HIVE-15839
> URL: https://issues.apache.org/jira/browse/HIVE-15839
> Project: Hive
> Issue Type: Sub-task
> Components: Query Planning, Query Processor, Transactions
> Affects Versions: 2.2.0
> Reporter: Eugene Koifman
> Assignee: Eugene Koifman
> Priority: Minor
> Attachments: HIVE-15839.01.patch, HIVE-15839.02.patch,
> HIVE-15839.03.patch
>
>
> should've been part of HIVE-14949
> if only WHEN NOT MATCHED is specified then the join is basically an anti-join
> and we are not retrieving any values from target side. So the cardinality
> check is just overhead (though presumably very minor since the filter above
> the join will filter everything and thus there is nothing to group)
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