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https://issues.apache.org/jira/browse/PHOENIX-3773?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16021409#comment-16021409
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James Taylor commented on PHOENIX-3773:
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Thanks for the patch, [~singamteja]. Here's some feedback:
- Make sure your code base has been rebased and that the patch applies. There
are directions here:
https://phoenix.apache.org/contributing.html#Generate_a_patch
- Have FIRST_VALUES return an ARRAY type so that you can return all values in a
single row. It's not going to work to change the semantics of SQL (it's pretty
well established). A function can't return multiple rows like that.
- Implement this in a base class so that you can support both FIRST_VALUES and
LAST_VALUES. It's a trivial matter of multiplying the result of the comparator
by -1 for LAST_VALUES.
> Implement FIRST_VALUES aggregate function
> -----------------------------------------
>
> Key: PHOENIX-3773
> URL: https://issues.apache.org/jira/browse/PHOENIX-3773
> Project: Phoenix
> Issue Type: New Feature
> Reporter: James Taylor
> Assignee: Loknath Priyatham Teja Singamsetty
> Labels: SFDC
> Fix For: 4.11.0
>
> Attachments: PHOENIX-3773.patch, PHOENIX-3773.v2.patch
>
>
> 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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