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Date: Wed, 17 Oct 2012 21:28:04 +0000 (UTC)
From: "Aaron Tokhy (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-4435) Add Group By functionality using
 Coprocessors
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    [ https://issues.apache.org/jira/browse/HBASE-4435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13478408#comment-13478408 ] 

Aaron Tokhy commented on HBASE-4435:
------------------------------------

Thanks for the quick review, I'll soon update JIRA with a new patch, based off of SVN trunk, though not at the moment.  Also I'll have to clean up some of the code, thanks for the quick feedback!

I may also change a few other things, such as using HashedBytes instead of Text to be able to perform roll-ups of types other than UTF-8 strings.
                
> Add Group By functionality using Coprocessors
> ---------------------------------------------
>
>                 Key: HBASE-4435
>                 URL: https://issues.apache.org/jira/browse/HBASE-4435
>             Project: HBase
>          Issue Type: Improvement
>          Components: Coprocessors
>            Reporter: Nichole Treadway
>            Priority: Minor
>              Labels: by, coprocessors, group, hbase
>         Attachments: HBase-4435.patch, HBASE-4435-v2.patch
>
>
> Adds in a Group By -like functionality to HBase, using the Coprocessor framework. 
> It provides the ability to group the result set on one or more columns (groupBy families). It computes statistics (max, min, sum, count, sum of squares, number missing) for a second column, called the stats column. 
> To use, I've provided two implementations.
> 1. In the first, you specify a single group-by column and a stats field:
>       statsMap = gbc.getStats(tableName, scan, groupByFamily, groupByQualifier, statsFamily, statsQualifier, statsFieldColumnInterpreter);
> The result is a map with the Group By column value (as a String) to a GroupByStatsValues object. The GroupByStatsValues object has max,min,sum etc. of the stats column for that group.
> 2. The second implementation allows you to specify a list of group-by columns and a stats field. The List of group-by columns is expected to contain lists of {column family, qualifier} pairs. 
>       statsMap = gbc.getStats(tableName, scan, listOfGroupByColumns, statsFamily, statsQualifier, statsFieldColumnInterpreter);
> The GroupByStatsValues code is adapted from the Solr Stats component.

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