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https://issues.apache.org/jira/browse/CALCITE-3091?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16848543#comment-16848543
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Stamatis Zampetakis commented on CALCITE-3091:
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Multiple default schemas sounds a bit weird and I am afraid it might confuse 
people. As you said, I don't think there are many people who need this kind of 
functionality so I guess we should avoid it.

If at the root level you declare 1 property with 5 schemas or in the 5 schemas 
you declare 1 property doesn't seem you are gaining much. Possibly you have a 
concrete example in mind, in that case please give provide a sample json file 
of how you would like to express things and then we can discuss further. 

> Expose defaultSchema .json parameter to SchemaFactory
> -----------------------------------------------------
>
>                 Key: CALCITE-3091
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3091
>             Project: Calcite
>          Issue Type: Improvement
>          Components: jdbc-adapter
>    Affects Versions: 1.19.0
>            Reporter: Ivan Grgurina
>            Priority: Major
>
> Currently, when you use JDBC adapter and have custom schema factory, you 
> provide .json file with your schema definition and link to your SchemaFactory 
> implementation that is called to create that Schema for the rest of the 
> system. 
> That .json file has in root a 'defaultSchema' parameter that Calcite uses to 
> know what the default schema is. Unfortunately, that parameter is not exposed 
> when implementing SchemaFactory interface, and there are use cases where that 
> would be useful.
> For example, one use case is when having multiple custom schemas, to know 
> which one is the default one while you're creating it inside SchemaFactory 
> implementation.
> My specific use-case is I want to use that .json parameter for "filtering" 
> schemas. The current workaround for that is to have two SchemaFactory 
> implementations that are then later connected in code, but it would be easier 
> if I could just check in SchemaFactory if my schema is the defaultSchema and 
> do the appropriate logic there.
> I'm willing to do the work to make this change if someone can point me in the 
> right direction.



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