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From "Ashutosh Chauhan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-8558) CBO: enable n-way joins after CBO join reordering
Date Wed, 22 Oct 2014 15:36:34 GMT

    [ https://issues.apache.org/jira/browse/HIVE-8558?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14180058#comment-14180058
] 

Ashutosh Chauhan commented on HIVE-8558:
----------------------------------------

+1

> CBO: enable n-way joins after CBO join reordering
> -------------------------------------------------
>
>                 Key: HIVE-8558
>                 URL: https://issues.apache.org/jira/browse/HIVE-8558
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Harish Butani
>            Assignee: Harish Butani
>         Attachments: HIVE-8558.1.patch
>
>
> With CBO, we disable n-way joins.  But for consecutive tables we can safely collapse
into n-way joins. For e.g this is safe to collapse:
> {code}
> select p1.p_name, p2.p_name, p3.p_name from part p1 join part p2 on p1.p_name = p2.p_name
join part p3 on p3.p_name = p1.p_name;
> {code}
> whereas, we shouldn't reorder in this case:
> {code}
> select p1.p_name, p2.p_name, p3.p_name 
> from part p1 join part p2 on p1.p_name = p2.p_name join part p3 on p3.p_size = p1.p_size
and p3.p_size = p2.p_size join part p4 on p1.p_name = p4.p_name;
> {code}



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