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Posted to issues@calcite.apache.org by "Julian Hyde (Jira)" <ji...@apache.org> on 2024/11/02 16:33:00 UTC

[jira] [Commented] (CALCITE-6665) Add isEmpty metadata to check if a relational expression returns no rows

    [ https://issues.apache.org/jira/browse/CALCITE-6665?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17895020#comment-17895020 ] 

Julian Hyde commented on CALCITE-6665:
--------------------------------------

Should the method also indicate whether the relation is never empty?

> Add isEmpty metadata to check if a relational expression returns no rows
> ------------------------------------------------------------------------
>
>                 Key: CALCITE-6665
>                 URL: https://issues.apache.org/jira/browse/CALCITE-6665
>             Project: Calcite
>          Issue Type: Improvement
>            Reporter: xiong duan
>            Priority: Major
>
> In Calcite, there are many times to determine whether a relational expression returns 0 rows through maxRowCount.
> But some places use `maxRowCount<=1D` while others use `maxRowCount ==0D`.
> This PR mainly aims to add `@Nullable Boolean RelMetadataQuery.isEmpty(RelNode)` to unify this behavior.



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