[jira] [Created] (FLINK-16195) append constant field to unique key set on project when deriving unique keys in FlinkRelMdUniqueKeys

[Shang Yuanchun (Jira)]

godfrey he created FLINK-16195:
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             Summary: append constant field to unique key set on project when deriving unique keys in FlinkRelMdUniqueKeys
                 Key: FLINK-16195
                 URL: https://issues.apache.org/jira/browse/FLINK-16195
             Project: Flink
          Issue Type: Improvement
          Components: Table SQL / Planner
            Reporter: godfrey he


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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