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From "Dudu Markovitz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-11022) Support collecting lists in user defined order
Date Sat, 30 Jul 2016 19:20:20 GMT

    [ https://issues.apache.org/jira/browse/HIVE-11022?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15400781#comment-15400781
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Dudu Markovitz commented on HIVE-11022:
---------------------------------------

In order to support complex ordering expressions I would suggest to add the sorting option
as an enhanced syntax for the current functions and not as additional functions, in a similar
way to MySQL's GROUP_CONCAT or Oracle's LISTAGG.
It would also be nice to add the SEPARATOR /DELIMITER option.

http://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html#function_group-concat
http://docs.oracle.com/cd/E11882_01/server.112/e41084/functions089.htm#SQLRF30030




> Support collecting lists in user defined order
> ----------------------------------------------
>
>                 Key: HIVE-11022
>                 URL: https://issues.apache.org/jira/browse/HIVE-11022
>             Project: Hive
>          Issue Type: New Feature
>          Components: UDF
>            Reporter: Michael Haeusler
>
> Hive currently supports aggregation of lists "in order of input rows" with the UDF collect_list.
Unfortunately, the order is not well defined when map-side aggregations are used.
> Hive could support collecting lists in user-defined order by providing a UDF
> COLLECT_LIST_SORTED(valueColumn, sortColumn[, limit]), that would return a list of values
sorted in a user defined order. An optional limit parameter can restrict this to the n first
values within that order.
> Especially in the limit case, this can be efficiently pre-aggregated and reduces the
amount of data transferred to reducers.



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