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