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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3715) float and double calculation is inaccurate in Hive
Date Tue, 18 Dec 2012 06:52:17 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13534708#comment-13534708
] 

Namit Jain commented on HIVE-3715:
----------------------------------

Have you looked at ArciMath BigDecimal - I have not looked at it, but casual browsing suggests
it might be faster than BigDecimal.
                
> float and double calculation is inaccurate in Hive
> --------------------------------------------------
>
>                 Key: HIVE-3715
>                 URL: https://issues.apache.org/jira/browse/HIVE-3715
>             Project: Hive
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 0.10.0
>            Reporter: Johnny Zhang
>            Assignee: Johnny Zhang
>         Attachments: HIVE-3715.patch.txt
>
>
> I found this during debug the e2e test failures. I found Hive miss calculate the float
and double value. Take float calculation as an example:
> hive> select f from all100k limit 1;
> 48308.98
> hive> select f/10 from all100k limit 1;
> 4830.898046875   <--added 04875 in the end
> hive> select f*1.01 from all100k limit 1;
> 48792.0702734375  <--should be 48792.0698
> It might be essentially the same problem as http://effbot.org/pyfaq/why-are-floating-point-calculations-so-inaccurate.htm.
But since e2e test compare the results with mysql and seems mysql does it right, so it is
worthy fixing it in Hive.

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