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https://issues.apache.org/jira/browse/PHOENIX-1580?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14366274#comment-14366274
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Alicia Ying Shu commented on PHOENIX-1580:
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UNION ALL is mostly used when you would like to access different tables, thus
likely different CFs. SubSelects in UNION ALL are executed in parallel and in
streaming fashion. Caching a large amount of CF data for multiple subselects
may not be feasible and can be expensive too. If CF data is small, scan them
should be fast.
> Support UNION ALL
> -----------------
>
> Key: PHOENIX-1580
> URL: https://issues.apache.org/jira/browse/PHOENIX-1580
> Project: Phoenix
> Issue Type: Bug
> Reporter: Alicia Ying Shu
> Assignee: Alicia Ying Shu
> Attachments: phoenix-1580.patch, unionall-wipe.patch
>
>
> Select * from T1
> UNION ALL
> Select * from T2
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