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From "Victoria Markman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-3429) DrillAvgVarianceConvertlet may produce wrong results while rewriting stddev, variance
Date Thu, 17 Dec 2015 18:32:46 GMT

    [ https://issues.apache.org/jira/browse/DRILL-3429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15062498#comment-15062498
] 

Victoria Markman commented on DRILL-3429:
-----------------------------------------

Verified fixed in 1.4.0

{code}
#Tue Dec 15 23:00:30 UTC 2015
git.commit.id.abbrev=2fbe668
git.commit.user.email=parthc@apache.org
git.commit.message.full=DRILL-4152\: Add trace logging to  Parquet reader for performance
tuning.\n
git.commit.id=2fbe668e8dcb3d06f345feb32a3d2ab1559f3645
{code}

Tests added in: Functional/window_functions/statistical_aggregates

> 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: Mehant Baid
>            Priority: Critical
>             Fix For: 1.3.0
>
>         Attachments: DRILL-3429.patch
>
>
> 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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