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From "Fabian Hueske (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4604) Add support for standard deviation/variance
Date Fri, 21 Oct 2016 16:24:58 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15595581#comment-15595581

Fabian Hueske commented on FLINK-4604:

Hi [~anmu],

I think we can implement and add support for {{SqlKind.SUM0}} as part of this issue.
For that you have to implement a custom {{Sum0Aggregate}} which extends {{SumAggregate}} and
overrides the {{prepare()}} method such that it does not initialize the aggregate with {{null}}
but with {{0}} if the value is {{null}}.

Next you have to fix the {{AggregateUtil}} and separate {{SqlSumEmptyIsZeroAggFunction}} from
{{SqlSumAggFunction}} and initialize the new {{Sum0Aggregate}} and also allow for {{case SqlKind.SUM0
=> true}} in {{DataSetAggregateRule}}.

If I did not forget a place to add SUM0 support, that should do the trick.

> Add support for standard deviation/variance
> -------------------------------------------
>                 Key: FLINK-4604
>                 URL: https://issues.apache.org/jira/browse/FLINK-4604
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Timo Walther
>            Assignee: Anton Mushin
>         Attachments: 1.jpg
> Calcite's {{AggregateReduceFunctionsRule}} can convert SQL {{AVG, STDDEV_POP, STDDEV_SAMP,
VAR_POP, VAR_SAMP}} to sum/count functions. We should add, test and document this rule. 
> If we also want to add this aggregates to Table API is up for discussion.

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