[jira] [Commented] (HIVE-6189) Support top level union all statements

["Lefty Leverenz (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-6189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14009674#comment-14009674 ] 

Lefty Leverenz commented on HIVE-6189:
--------------------------------------

[~hagleitn], how's this wiki revision?

* [Language Manual - Union | https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Union]
* [diffs | https://cwiki.apache.org/confluence/pages/diffpages.action?pageId=27362049&originalId=41812730]

> 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
>             Fix For: 0.13.0
>
>         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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