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https://issues.apache.org/jira/browse/HIVE-647?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12732231#action_12732231
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Ashish Thusoo commented on HIVE-647:
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Actually sort is supposed to be a local sort within a reduce instead of a
global sort. It is usually used along with the distribute by to define the
manner in which the keys are distributed to a reducer and sorted within a
reducer.
I believe that if you used order by instead of sort by we automatically select
1 reducer and do the sort.
> SORT BY with GROUP ignored without LIMIT
> ----------------------------------------
>
> Key: HIVE-647
> URL: https://issues.apache.org/jira/browse/HIVE-647
> Project: Hadoop Hive
> Issue Type: Bug
> Components: Query Processor
> Reporter: Bill Graham
>
> For queries with GROUP BY and SORT BY, the sort is not handled properly when
> a LIMIT is not supplied. If I run the following two queries, the first
> returns properly sorted results. The second does not.
> SELECT user, SUM(numRequests) AS num FROM MyTable GROUP BY user SORT BY num
> DESC LIMIT 50;
> SELECT user, SUM(numRequests) AS num FROM MyTable GROUP BY user SORT BY num
> DESC;
> Explain is different for the two queries as well. The first uses 3 M/R jobs
> and the second only uses 2, which might be part of the problem.
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