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From "Mehant Baid (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DRILL-3429) DrillAvgVarianceConvertlet may produce wrong results while rewriting stddev, variance
Date Mon, 19 Oct 2015 23:32:27 GMT

     [ https://issues.apache.org/jira/browse/DRILL-3429?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mehant Baid updated DRILL-3429:
-------------------------------
    Attachment:     (was: DRILL-3429.patch)

> DrillAvgVarianceConvertlet may produce wrong results while rewriting stddev, variance
> -------------------------------------------------------------------------------------
>
>                 Key: DRILL-3429
>                 URL: https://issues.apache.org/jira/browse/DRILL-3429
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Mehant Baid
>            Assignee: Aman Sinha
>            Priority: Critical
>             Fix For: 1.3.0
>
>
> DrillAvgVarianceConvertlet currently rewrites aggregate functions like avg, stddev, variance
to simple computations. 
> Eg: 
> Stddev( x ) => power(
>          (sum(x * x) - sum( x ) * sum( x ) / count( x ))
>          / count( x ),
>          .5)
> Consider the case when the input is an integer. Now the rewrite contains multiplication
and division, which will bind to functions that operate on integers however the expected result
should be a double and since double has more precision than integer we should be operating
on double during the multiplication and division.  



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