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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