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https://issues.apache.org/jira/browse/HIVE-707?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13593428#comment-13593428
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Svetozar Misljencevic commented on HIVE-707:
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You could use the currently undocumented union_map function as a workaround...
Try :
concat_ws(' ', map_keys(UNION_MAP(MAP(your_column, 'dummy'))))
> add group_concat
> ----------------
>
> Key: HIVE-707
> URL: https://issues.apache.org/jira/browse/HIVE-707
> Project: Hive
> Issue Type: New Feature
> Components: Query Processor
> Reporter: Namit Jain
> Assignee: Min Zhou
>
> Moving the discussion to a new jira:
> I've implemented group_cat() in a rush, and found something difficult to
> slove:
> 1. function group_cat() has a internal order by clause, currently, we can't
> implement such an aggregation in hive.
> 2. when the strings will be group concated are too large, in another words,
> if data skew appears, there is often not enough memory to store such a big
> result.
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