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https://issues.apache.org/jira/browse/HIVE-5657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13806508#comment-13806508
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Navis commented on HIVE-5657:
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Yes, top-n is not working with distincts. Test included in limit_pushdown.q was
not good enough to show the flaw. I'll check this later.
> TopN produces incorrect results with count(distinct)
> ----------------------------------------------------
>
> Key: HIVE-5657
> URL: https://issues.apache.org/jira/browse/HIVE-5657
> Project: Hive
> Issue Type: Bug
> Reporter: Sergey Shelukhin
> Priority: Critical
> Attachments: example.patch
>
>
> Attached patch illustrates the problem.
> limit_pushdown test has various other cases of aggregations and distincts,
> incl. count-distinct, that work correctly (that said, src dataset is bad for
> testing these things because every count, for example, produces one record
> only), so something must be special about this.
> I am not very familiar with distinct- code and these nuances; if someone
> knows a quick fix feel free to take this, otherwise I will probably start
> looking next week.
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