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Excerpts from Mike Bayer's message of 2014-10-04 08:10:38 -0700:
> 
> On Oct 4, 2014, at 1:10 AM, Kevin Benton <blak111 at gmail.com> wrote:
> 
> > Does sqlalchemy have good support for cross-database foreign keys? I was under the impression that they cannot be implemented with the normal syntax and semantics of an intra-database foreign-key constraint. 
> 
> cross “database” is not typically portable, but cross “schema” is.   
> 
> different database vendors have different notions of “databases” or “schemas”.
> 
> if you can get the “other database” to be accessible from the target database via “otherdatabase.sometable”, then you’re in.
> 
> from SQLAlchemy’s perspective, it’s just a name with a dot.   It’s the database itself that has to support the foreign key at the scope you are shooting for.
> 

All true, however, there are zero guarantees that databases will be
hosted on the same server, and typically permissions are setup to prevent
cross-schema joins.

Typically we use the public API's when we want to access data in a
different application. The database is a private implementation detail
of each application.