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https://issues.apache.org/jira/browse/CALCITE-3355?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16933010#comment-16933010
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Chunwei Lei commented on CALCITE-3355:
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[~kirillkozlov] , I would like to task this issue if you don't mind.

> Deduce whether CASE and COALESCE may produce NULL values
> --------------------------------------------------------
>
>                 Key: CALCITE-3355
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3355
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 1.20.0
>            Reporter: Kirill Kozlov
>            Priority: Major
>
> When executing queries like: 
> "SELECT COALESCE(name, 'unknown') as name_out FROM PCOLLECTION"
> (input 'name' is nullable)
> There is a need to know whether the result is nullable or not (in this case - 
> not). During validation stage "COALESCE" is being transformed (via 
> SqlValidatorImpl.performUnconditionalRewrites) into a "CASE" statement, which 
> currently does not determine nullability of a result.



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