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From "Phabricator (JIRA)" <>
Subject [jira] [Commented] (HIVE-3464) Merging join tree may reorder joins which could be invalid
Date Mon, 21 Jan 2013 07:06:14 GMT


Phabricator commented on HIVE-3464:

njain has commented on the revision "HIVE-3464 [jira] Merging join tree may reorder joins
which could be invalid".

  ql/src/test/queries/clientpositive/mergejoins_mixed.q:19 I am totally confused.

  What is the diff. between the above query and the first query in
  ql/src/java/org/apache/hadoop/hive/ql/parse/ Can you write a small
wiki/note on that explaining the correct behavior ?
  This is very difficult to review otherwise.


To: JIRA, navis
Cc: njain

> Merging join tree may reorder joins which could be invalid
> ----------------------------------------------------------
>                 Key: HIVE-3464
>                 URL:
>             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
> 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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