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https://issues.apache.org/jira/browse/HBASE-4435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13255546#comment-13255546
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lifeng commented on HBASE-4435:
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when can this patch be put into hbase?
> 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
> Attachments: HBase-4435.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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