[jira] [Commented] (PHOENIX-3773) Implement FIRST_VALUES aggregate function

["James Taylor (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-3773?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15961544#comment-15961544 ] 

James Taylor commented on PHOENIX-3773:
---------------------------------------

FYI, [~singamteja]

> Implement FIRST_VALUES aggregate function
> -----------------------------------------
>
>                 Key: PHOENIX-3773
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-3773
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: James Taylor
>              Labels: SFDC
>
> Similar to FIRST_VALUE, but would allow the user to specify how many values to keep. This could use a MinMaxPriorityQueue under the covers and be much more efficient than using multiple NTH_VALUE calls to do the same like this:
> {code}
> SELECT entity_id,
>        NTH_VALUE(user_id,1) WITHIN GROUP (ORDER BY last_read_date DESC) as nth1_user_id,
>        NTH_VALUE(user_id,2) WITHIN GROUP (ORDER BY last_read_date DESC) as nth2_user_id,
>        NTH_VALUE(user_id,3) WITHIN GROUP (ORDER BY last_read_date DESC) as nth3_user_id,
>        count(*)
> FROM  MY_TABLE 
> WHERE tenant_id='00Dx0000000XXXX'
> AND entity_id in ('0D5x000000ABCD','0D5x000000ABCE')
> GROUP BY entity_id;
> {code}



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