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From "Ning Zhang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-887) Allow SELECT <col> without a mapreduce job
Date Tue, 19 Jan 2010 05:48:54 GMT

    [ https://issues.apache.org/jira/browse/HIVE-887?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12802105#action_12802105
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Ning Zhang commented on HIVE-887:
---------------------------------

Eric, we were discussing the same thing before to allow simple where-clause to the non-MR
client side execution. This woud be straightforward after we make fetchOperator extends Operator.
Then basically any map-only plan (including map-side joins) could be move to non-MR execution.


The only thing I'm not sure about is the "fetch n" syntax. Since we don't have stats, we don't
know the number of rows in the input file. So as a first step we can rely on the file size.


> Allow SELECT <col> without a mapreduce job
> ------------------------------------------
>
>                 Key: HIVE-887
>                 URL: https://issues.apache.org/jira/browse/HIVE-887
>             Project: Hadoop Hive
>          Issue Type: New Feature
>         Environment: All
>            Reporter: Eric Sun
>            Assignee: Ning Zhang
>
> I often find myself needing to take a quick look at a particular column of a Hive table.
> I usually do this by doing a 
> SELECT * from <table> LIMIT 20;
> from the CLI.  Doing this is pretty fast since it doesn't require a mapreduce job.  However,
it's tough to examine just 1 or 2 columns when the table is very wide.
> So, I might do
> SELECT <col> from <table> LIMIT 20;
> but it's much slower since it requires a map-reduce.  It'd be really convenient if a
map-reduce wasn't necessary.
> Currently a good work around is to do
> hive -e "select * from table" | cut --key=n
> but it'd be more convenient if it were built in since it alleviates the need for column
counting.

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