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From "Gunther Hagleitner (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HIVE-6189) Support top level union all statements
Date Wed, 15 Jan 2014 00:53:26 GMT

     [ https://issues.apache.org/jira/browse/HIVE-6189?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Gunther Hagleitner updated HIVE-6189:
-------------------------------------

    Attachment: HIVE-6189.3.patch

Thanks [~navis] for the review. I've added .3 because [~rhbutani] showed me a much better
way to do this. He showed me how I can do all the necessary rewrites in the grammar without
having to mess with the tree in semantic analysis. This is much cleaner.

> Support top level union all statements
> --------------------------------------
>
>                 Key: HIVE-6189
>                 URL: https://issues.apache.org/jira/browse/HIVE-6189
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Gunther Hagleitner
>            Assignee: Gunther Hagleitner
>         Attachments: HIVE-6189.1.patch, HIVE-6189.2.patch, HIVE-6189.3.patch
>
>
> I've always wondered why union all has to be in subqueries in hive.
> After looking at it, problems are:
> - Hive Parser:
>   - Union happens at the wrong place (insert ... select ... union all select ...) is
parsed as (insert select) union select.
>   - There are many rewrite rules in the parser to force any query into the a from - insert
-select form. No doubt for historical reasons.
> - Plan generation/semantic analysis assumes top level "TOK_QUERY" and not top level "TOK_UNION".
> The rewrite rules don't work when we move the "UNION ALL" recursion into the select statements.
However, it's not hard to do that in code.



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