Foreign Data Wrapper - PostgreSQL Developer's Guide - page 212

Working with postgres_fdw
PostgreSQL provides a template to create your own foreign data wrapper, and
there are many foreign data wrappers available on the Internet. But there are only
two oficially supported foreign data wrappers: postgres_fdw and file_fdw . The
postgres_fdw is a foreign data wrapper that is used to retrieve and manipulate
the remote PostgreSQL's server. The postgres_fdw data wrapper can be used by
performing the following steps:

1. Load the extension using CREATE EXTENSION :

postgres=# CREATE EXTENSION postgres_fdw;

2. Create the server using CREATE SERVER :

postgres=# CREATE SERVER postgres_server FOREIGN DATA
WRAPPER postgres_fdw OPTIONS (host, '127.0.0.1',
port '5432', dbname 'postgres');

3. Create user mapping using CREATE USER MAPPING :

postgres=# CREATE USER MAPPING FOR PUBLIC SERVER
postgres_server;

4. Create a foreign table using CREATE FOREIGN TABLE :

postgres=# CREATE FOREIGN TABLE dummy_table (foo INTEGER,
bar TEXT) SERVER postgres_server OPTIONS
(table_name 'remote_dummy_table');

5. Insert data into the foreign table:

postgres=# INSERT INTO dummy_table VALUES (1, 'foo');

6. Select data from the foreign data wrapper:

postgres=# SELECT * FROM dummy_table;
foo | bar
-----+-----
(0 rows)

Working with ile_fdw
The file_fdw data wrapper is another oficially supported foreign data wrapper.
This is used to access the iles in the server ile system. The file_fdw data wrapper
can be used by performing the following steps:

1. Load extension using CREATE EXTENSION :

postgres=# CREATE EXTENSION file_fdw;