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https://issues.apache.org/jira/browse/FLINK-16195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17041616#comment-17041616
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Jark Wu commented on FLINK-16195:
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What's the problem when we don't have the additional "a, b, 1" unique key in
the set?
> Append constant fields to unique key set when deriving unique keys in
> FlinkRelMdUniqueKeys on project
> -----------------------------------------------------------------------------------------------------
>
> Key: FLINK-16195
> URL: https://issues.apache.org/jira/browse/FLINK-16195
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Planner
> Reporter: godfrey he
> Assignee: godfrey he
> Priority: Major
>
> currently, {{FlinkRelMdUniqueKeys}} only supports deriving unique keys on
> non-constant fields. such as: {{select a, b, 1, count( * ) from T group by a,
> b}}, currently the derived unique keys is {{a, b}}. However {{a, b, 1}} is
> also a unique key, and the result is {{a, b}} and {{a, b, 1}}.
> note: Ideally, the planner does not require the constant key in the unique
> key set, all constant values are pulled up or removed as much as possible.
> Supports this improvement to handle some corner cases in cbo.
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