On Fri, 27 Mar 2009, Mauro Bertoli wrote:
> SELECT
> db1.a.id FROM db1.a
> UNION
> db2.b.id FROM db2.b
>
> Where "db1" is a database and "db2" is another database. "a" is a
> table in database "db1" and "b" is a table in database "db2"
You might be able to create the equivalent of a union by having a
front-end program connect to both databases. You can have two open
connections and query them in turn and put the union together.
Particularly if it is just a union of keys.
But the essential idea is that the database is the universe of data.
E.g. you want to minimize data redundancy in a db, but you wouldn't
want to do that across databases, because they are different,
independent worlds. What is the business of one is not the business
of the other.
A query like the above seems to defeat this idea. What you are
calling databases, or what the other DBMS calls databases, arguably
are not.
--
Elle