Multidatabase query

Hi Mauro,

Not possible in PostgreSQL.

However, you can use dblink for creating query between multidatabase as
given below:

select empno from dblink('dbname=edb','SELECT empno from emp') as
emp(empno numeric)
union
select empno from dblink('dbname=enterprisedb','SELECT empno from emp')
as emp(empno numeric);

where edb and enterprisedb are database names

For More information about dblink, please follow the link given below:
http://www.postgresql.org/docs/current/static/dblink.html
http://www.enterprisedb.com/docs/en/8.3/oracompat/EnterpriseDB_OraCompat_EN_8.3-49.htm

Regards,
Vibhor Kumar
www.enterprisedb.com

Mauro Bertoli wrote:

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