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Posted to issues@flink.apache.org by "Kurt Young (JIRA)" <ji...@apache.org> on 2019/01/30 13:49:00 UTC
[jira] [Commented] (FLINK-8594) Add a dedicated DISTINCT operator
to always produce append sreams
[ https://issues.apache.org/jira/browse/FLINK-8594?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16756123#comment-16756123 ]
Kurt Young commented on FLINK-8594:
-----------------------------------
I'm closing this issue since it will be addressed after blink gets merged.
> Add a dedicated DISTINCT operator to always produce append sreams
> -----------------------------------------------------------------
>
> 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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