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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4086) Add limit to Hive QL
Date Tue, 16 Sep 2008 06:25:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4086?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12631263#action_12631263
] 

Joydeep Sen Sarma commented on HADOOP-4086:
-------------------------------------------

one thing i found fairly ridiculous is that the current select * from <blah> actually
runs a map-reduce job. we have to fix this :-).

if the LimitMapOp can be run in a separate client side task that dumps to console instead
of to a file (in case we are not emitting to a table) - that would kill two birds with one
stone.

the limit in the inner clause is interesting. how we wish there was a no-sort option for map-reduce!
the sorting is high overhead - so a separate concatenator task (which may still be run on
the cluster where the concatenation runs inside a single mapper no-reducer map-reduce job)
may be better. (that is assuming we are doing a redundant sort - which may not be true in
all cases).

> Add limit to Hive QL
> --------------------
>
>                 Key: HADOOP-4086
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4086
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: contrib/hive
>            Reporter: Ashish Thusoo
>            Assignee: Ashish Thusoo
>
> Add a limit feature to the Hive Query language.
> so you can do the following things:
> SELECT * FROM T LIMIT 10;
> and this would just return the 10 rows.
> No gaurantees are made on which 10 rows are returned by the query.

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