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https://issues.apache.org/jira/browse/FLINK-8594?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16628930#comment-16628930
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Timo Walther commented on FLINK-8594:
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[~hequn8128] what is the status of this issue? I also wondered why a {{SELECT
DISTINCT}} is not an append stream.
> Make producesUpdates in DataStreamGroupAggregate return false if it is a
> distinct group by without state retention configuration
> ---------------------------------------------------------------------------------------------------------------------------------
>
> Key: FLINK-8594
> URL: https://issues.apache.org/jira/browse/FLINK-8594
> Project: Flink
> Issue Type: Improvement
> Components: Table API & SQL
> Reporter: Hequn Cheng
> Assignee: Hequn Cheng
> Priority: Major
>
> Internally, the {{DISTINCT}} is translated into a {{GROUP BY}} with all
> distinct fields being keys and no aggregation functions. However, this kind
> of \{{GROUP BY}} don't generate update at all if the state retention time has
> not been configured. We can treat the result table as an append table.
> Therefore, we can make the \{{producesUpdates}} function return false, so the
> downstream group by will not choose the correspond retract agg function,
> i.e., {{MaxWithRetractAggFunction}}
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