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https://issues.apache.org/jira/browse/TAJO-1514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14394126#comment-14394126
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Keuntae Park commented on TAJO-1514:
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Upon the definition of UNION and UNION ALL,
UNION is equivalent to apply DISTINCT to the result of UNION ALL.
So, I'm going to handle UNION by rewriting as UNION ALL + GROUP BY.
Hive also implements UNION by rewriting it to UNION ALL followed by GROUP BY in
HIVE-9039.
> Distinguishing UNION and UNION ALL
> ----------------------------------
>
> Key: TAJO-1514
> URL: https://issues.apache.org/jira/browse/TAJO-1514
> Project: Tajo
> Issue Type: Sub-task
> Reporter: Keuntae Park
> Assignee: Keuntae Park
>
> Currently, Tajo handles both UNION and UNION ALL as UNION ALL.
> For UNION, however, result should not have duplicated rows.
> It needs to handle them differently.
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