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