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Date: Fri, 13 Dec 2013 15:38:07 +0000 (UTC)
From: "Xuefu Zhang (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
Message-ID: <JIRA.12683761.1386647171922.32603.1386949087681@arcas>
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Subject: [jira] [Commented] (HIVE-5996) Query for sum of a long column of a
 table with only two rows produces wrong result
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    [ https://issues.apache.org/jira/browse/HIVE-5996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13847579#comment-13847579 ] 

Xuefu Zhang commented on HIVE-5996:
-----------------------------------

Yes, in theory, but unlikely. Current precision formula, 10 + p as the output precision, gives some room. Of course, if the input precision is already at  maximum, then output type precision will the same as the input precision. In that case, for really big numbers, it can overflow. Anyway, I'm going to close the JIRA, so the discussion.

> Query for sum of a long column of a table with only two rows produces wrong result
> ----------------------------------------------------------------------------------
>
>                 Key: HIVE-5996
>                 URL: https://issues.apache.org/jira/browse/HIVE-5996
>             Project: Hive
>          Issue Type: Bug
>          Components: UDF
>    Affects Versions: 0.12.0
>            Reporter: Xuefu Zhang
>            Assignee: Xuefu Zhang
>         Attachments: HIVE-5996.patch
>
>
> {code}
> hive> desc test2;
> OK
> l                   	bigint              	None                
> hive> select * from test2;                                 
> OK
> 6666666666666666666
> 5555555555555555555
> hive> select sum(l) from test2;
> OK
> -6224521851487329395
> {code}
> It's believed that a wrap-around error occurred. It's surprising that it happens only with two rows. Same query in MySQL returns:
> {code}
> mysql> select sum(l) from test;
> +----------------------+
> | sum(l)               |
> +----------------------+
> | 12222222222222222221 |
> +----------------------+
> 1 row in set (0.00 sec)
> {code}
> Hive should accommodate large number of rows. Overflowing with only two rows is very unusable.


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