Use PostgreSQL to query across databases
PostgreSQL itself does not natively support cross-database queries, as the error message indicates, but there are some workarounds available. One way is to use the postgres_fdw
extension.
postgres_fdw
postgres_fdw
(foreign data wrapper) allows you to connect to a table in any PostgreSQL database, regardless of its location. To use this extension:
-
Make sure your version of Postgres supports
postgres_fdw
(v9.3 or higher recommended). -
Install the
postgres_fdw
extension in each database where you wish to perform cross-database queries. -
Create external server and user mapping:
postgres=# CREATE SERVER foreign_server FOREIGN DATA WRAPPER postgres_fdw OPTIONS (host 'remote_host', port '5432'); postgres=# CREATE USER MAPPING FOR CURRENT_USER SERVER foreign_server OPTIONS (user 'remote_user', password 'remote_password');
-
Create external table:
postgres=# CREATE FOREIGN TABLE cross_db_table SERVER foreign_server OPTIONS (table_name 'remote_table');
Alternatives before version 9.3
For Postgres versions prior to 9.3, you can use a function named dblink
to perform cross-database queries. Although it is maintained and distributed together with PostgreSQL, its usage is different from postgres_fdw
. See the PostgreSQL documentation for more details on dblink
.
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