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From "Timo Walther (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4604) Add support for standard deviation/variance
Date Fri, 14 Oct 2016 13:25:20 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15575320#comment-15575320
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Timo Walther commented on FLINK-4604:
-------------------------------------

The problem is that the rule translates not only into {{SUM}} and {{COUNT}} but also into
{{SqlKind.SUM0}}/{{SqlSumEmptyIsZeroAggFunction}} which is not yet supported. This means we
need to adapt the {{AggregateUtil}} to support this aggregation first. If I use the normal
sum aggregator for it, I get the "Type NULL is not supported" exception. This is bug actually
a null within a {{CASE}} expression should have a type.

> 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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