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From "Mehant Baid (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-2870) Fix return type of aggregate functions to be nullable
Date Fri, 24 Apr 2015 22:13:39 GMT

    [ https://issues.apache.org/jira/browse/DRILL-2870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14511891#comment-14511891
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Mehant Baid commented on DRILL-2870:
------------------------------------

[~jnadeau] I can come up with a few alternatives but I wanted to point out that the running
type of the aggregate is still a required type. So we are not paying a cost on a per row basis,
the only difference is when we set the output vector we will have to do an additional set
operation in the bits vector to indicate value is not null. Since this happens only on at
a batch level it seems fine. 

> Fix return type of aggregate functions to be nullable
> -----------------------------------------------------
>
>                 Key: DRILL-2870
>                 URL: https://issues.apache.org/jira/browse/DRILL-2870
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Mehant Baid
>            Assignee: Aman Sinha
>            Priority: Critical
>             Fix For: 1.0.0
>
>         Attachments: DRILL-2870.patch
>
>
> The output type of aggregate functions is required if the input is required which does
not always hold true. Consider the case where input is a required type and we are performing
sum(), however if all the rows are filtered out then we should return null instead of 0. This
holds true for all aggregate functions (except count). 
> As part of DRILL-2277 we are fixing the case when we have an aggregate function (without
group by) and the input batch is empty we still need to produce one record with null as output
(count function is an exception to this). If we don't fix the return type of aggregate functions
then we will return wrong results in the case where we have an empty input with required columns.




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