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Date: Thu, 26 Mar 2009 14:39:50 -0700 (PDT)
From: "Zheng Shao (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
Subject: [jira] Commented: (HIVE-61) Implment ORDER BY
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    [ https://issues.apache.org/jira/browse/HIVE-61?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12689683#action_12689683 ] 

Zheng Shao commented on HIVE-61:
--------------------------------

Most of the use cases with total ordering is to get the top 10.

For getting the top 10, the current work-around is:

First store the top 10 from each partition to some temp table:
INSERT OVERWRITE tableB
REDUCE a.*
USING 'head -n 10'
AS (col1, col2, col3, col4, ...)
FROM (SELECT * FROM tableA SORT BY col3 DESC, col4 ASC) a

Second, set the #reducer to 1 and get the top 10 globally.
set mapred.reduce.tasks=1;
SELECT * FROM tableB SORT BY col3 DESC, col4 ASC LIMIT 10


> Implment ORDER BY
> -----------------
>
>                 Key: HIVE-61
>                 URL: https://issues.apache.org/jira/browse/HIVE-61
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Jeff Hammerbacher
>            Assignee: Zheng Shao
>
> ORDER BY is in the query language reference but currently is a no-op. We should make it an op.

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