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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3430) group by followed by join with the same key should be optimized
Date Wed, 05 Sep 2012 11:44:07 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13448651#comment-13448651
] 

Namit Jain commented on HIVE-3430:
----------------------------------

Consider the following query:

select * from
(
  select c.value, count(1) as cnt from
  (
    select b.key, b.value from
      (select key, length(value) from T1 where ds = '1') a
        join
      T2 b on b.ds = '1' and a.key = b.key
  ) c
  group by c.value
) d
join
(select value, count(1) as cnt from T2 c where c.ds = '1' group by value) e
on d.value = e.value;



Every join and group by above has a separate map-reduce job.

                
> group by followed by join with the same key should be optimized
> ---------------------------------------------------------------
>
>                 Key: HIVE-3430
>                 URL: https://issues.apache.org/jira/browse/HIVE-3430
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Namit Jain
>


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