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https://issues.apache.org/jira/browse/PHOENIX-2069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15125208#comment-15125208
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Swapna Kasula commented on PHOENIX-2069:
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Requirement Details:

Similar to aggregate functions we have like :SUM, COUNT, we need to have a 
feature for custom aggregate functions to be called in queries, which 
facilitates to implement any custom aggregation logic as per the need.

ex: Select customagg(column) from table where date>= 10152015 and date<10172015 
group by date;

customagg - is a custom aggregated function

This can be an extension to custom UDF.



> Support custom aggregate UDFs
> -----------------------------
>
>                 Key: PHOENIX-2069
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2069
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: James Taylor
>            Assignee: Rajeshbabu Chintaguntla
>              Labels: YARN-TLS
>
> We should build on our existing feature of custom UDFs to support custom 
> aggregate functions. We could drive the requirements initially from a YARN 
> use case to allow them to plugin a custom aggregator that would just be 
> passed the Tuple (i.e. List<Cell> for each row scanned) plus a context 
> object. The custom code code then do whatever aggregation is required and 
> we'd have a hook to serialize back out the per scan aggregation.



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