A foreign data wrapper for PostgreSQL is a plugin that allows PostgreSQL to access and query data from external sources as if it were a regular table in a local PostgreSQL database. This allows users to perform joins and other operations on external data using SQL, as well as integrate external data with local data in their queries. This can be useful for a variety of purposes, such as integrating data from multiple sources, or accessing data from external sources that are not natively supported by PostgreSQL.
To configure a foreign data wrapper for PostgreSQL, you will need to perform the following steps:
- Install the foreign data wrapper extension for PostgreSQL. This can typically be done using the
CREATE EXTENSIONcommand. For example:
CREATE EXTENSION postgres_fdw;
- Create a foreign server object that represents the external data source you want to access. This can be done using the
CREATE SERVERcommand. For example:
CREATE SERVER my_server
FOREIGN DATA WRAPPER postgres_fdw
OPTIONS (host 'my_server_hostname', port '5432');
- Create a user mapping for the foreign server. This step is required to specify which user account on the local PostgreSQL server will be used to connect to the foreign server. This can be done using the
CREATE USER MAPPINGcommand. For example:
CREATE USER MAPPING FOR current_user
SERVER my_server
OPTIONS (user 'my_server_username', password 'my_server_password');
- Create a foreign table that represents the external data you want to access. This can be done using the
CREATE FOREIGN TABLEcommand. For example:
CREATE FOREIGN TABLE my_table (
id INTEGER,
name TEXT
) SERVER my_server
OPTIONS (table_name 'my_table');
After completing these steps, you should be able to query the foreign table using regular SQL commands as if it were a local table in your PostgreSQL database. For example:
SELECT * FROM my_table;
Note that the exact steps for configuring a foreign data wrapper may vary depending on the specific foreign data wrapper and the details of your setup. Consult the documentation for the specific foreign data wrapper you are using for more information.
