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https://issues.apache.org/jira/browse/CALCITE-2673?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16687262#comment-16687262
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Stamatis Zampetakis commented on CALCITE-2673:
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Can't we use the DatabaseMetadata#getFunctions to populate the Schema with the 
existing functions provided by the database? Then we could possibly add an 
appropriate method in RelOptSchema so that the rules have access to the defined 
functions. Just an idea, I don't know if it is applicable to your use-case and 
if you are referring to some rule in the JdbcConvention.

> Default implementation of SqlDialect should not support pushing all functions
> -----------------------------------------------------------------------------
>
>                 Key: CALCITE-2673
>                 URL: https://issues.apache.org/jira/browse/CALCITE-2673
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>            Reporter: Jesus Camacho Rodriguez
>            Assignee: Jesus Camacho Rodriguez
>            Priority: Major
>             Fix For: 1.18.0
>
>
> SqlDialect contains a 'supportsFunction' that can be used by rules to know 
> whether a certain function is supported in the given dialect, e.g., to choose 
> whether to push a Filter expression to JDBC, etc.
> The default implementation of 'supportsFunction' always returns true.
> I believe a better idea would be to support in the default implementation for 
> the method the most common SQL functions. Then each dialect can override that 
> behavior and expand/limit the supported functions, e.g., JethroDataDialect 
> already does that.



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