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From "Gunther Hagleitner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-5658) count(distinct) produces confusing results for null
Date Sat, 26 Oct 2013 06:05:30 GMT

    [ https://issues.apache.org/jira/browse/HIVE-5658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13806011#comment-13806011
] 

Gunther Hagleitner commented on HIVE-5658:
------------------------------------------

[~sershe]: Fear not, captain null is here :-P

This is not a bug - it's correct behavior. Count distinct is supposed to count all non-null
unique expressions, which is 0 for the null group in your query. 

> count(distinct) produces confusing results for null
> ---------------------------------------------------
>
>                 Key: HIVE-5658
>                 URL: https://issues.apache.org/jira/browse/HIVE-5658
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Sergey Shelukhin
>
> {code}
> select csmallint, count(distinct(csmallint)) from alltypesorc group by csmallint limit
3;
> {code}
> produces:
> {noformat}
> NULL	0
> -16379	1
> -16373	1
> {noformat}
> There are records in table with NULL values; however the count in this case should be
1, not 0, it seems. This is with TopN disabled, so it is unrelated to the other bug



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