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From "Ashutosh Chauhan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3464) Merging join tree may reorder joins which could be invalid
Date Tue, 02 Apr 2013 21:45:17 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3464?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13620306#comment-13620306
] 

Ashutosh Chauhan commented on HIVE-3464:
----------------------------------------

+1 will commit if tests pass.
                
> Merging join tree may reorder joins which could be invalid
> ----------------------------------------------------------
>
>                 Key: HIVE-3464
>                 URL: https://issues.apache.org/jira/browse/HIVE-3464
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.10.0
>            Reporter: Navis
>            Assignee: Navis
>         Attachments: HIVE-3464.D5409.2.patch, HIVE-3464.D5409.3.patch, HIVE-3464.D5409.4.patch,
HIVE-3464.D5409.5.patch, HIVE-3464.D5409.6.patch
>
>
> Currently, hive merges join tree from right to left regardless of join types, which may
introduce join reordering. For example,
> select * from a join a b on a.key=b.key join a c on b.key=c.key join a d on a.key=d.key;

> Hive tries to merge join tree in a-d=b-d, a-d=a-b, b-c=a-b order and a-d=a-b and b-c=a-b
will be merged. Final join tree is "a-(bdc)".
> With this, ab-d join will be executed prior to ab-c. But if join type of -c and -d is
different, this is not valid.

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