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From "Ashutosh Chauhan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-8298) Incorrect results for n-way join when join expressions are not in same order across joins
Date Tue, 30 Sep 2014 01:33:36 GMT

    [ https://issues.apache.org/jira/browse/HIVE-8298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14152687#comment-14152687
] 

Ashutosh Chauhan commented on HIVE-8298:
----------------------------------------

Issue is that while merging this n-way join we copied expressions from one join tree into
another without paying attention to fact that they could be in different order. There are
two workarounds for it:
* Introduce any udf on join condition like cast column to string.
* Rewrite the query so that expressions are in same order in two join.

First one disables the join merge altogether, thereby avoiding buggy code-path. So, it will
avoid the bug but will result in 2 jobs and thereby suboptimal performance. Second one is
a better workaround since join merging will still happen, but since original order of expressions
is maintained, bug doesn't kick in. 

> Incorrect results for n-way join when join expressions are not in same order across joins
> -----------------------------------------------------------------------------------------
>
>                 Key: HIVE-8298
>                 URL: https://issues.apache.org/jira/browse/HIVE-8298
>             Project: Hive
>          Issue Type: Bug
>          Components: Logical Optimizer
>    Affects Versions: 0.13.0, 0.13.1
>            Reporter: Ashutosh Chauhan
>            Assignee: Ashutosh Chauhan
>            Priority: Blocker
>
> select count( * ) from srcpart a join srcpart b on a.key = b.key and a.hr = b.hr join
srcpart c on a.hr = c.hr and a.key = c.key;
> is minimal query which reproduces it



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