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https://issues.apache.org/jira/browse/CALCITE-6027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17769917#comment-17769917
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Julian Hyde commented on CALCITE-6027:
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You don't need a special rule. Just do constant reduction.
> Add the rule to rewrite cardinality on map_keys and map_values functions
> ------------------------------------------------------------------------
>
> Key: CALCITE-6027
> URL: https://issues.apache.org/jira/browse/CALCITE-6027
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Affects Versions: 1.35.0
> Reporter: Ran Tao
> Assignee: Ran Tao
> Priority: Major
>
> when we call cardinality on map_keys or map_values, such as:
> {code:java}
> select cardinality(map_keys(map['foo', 1, 'bar', 2]));
> select cardinality(map_values(map['foo', 1, 'bar', 2]));{code}
> they can be safely simplified to
> {code:java}
> select cardinality(map['foo', 1, 'bar', 2]);
> select cardinality(map['foo', 1, 'bar', 2]); {code}
>
> Some other mature engines such as presto/trino has same optimized logic.
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