CREATE FOREIGN DATA WRAPPER name [ VALIDATOR valfunction | NO VALIDATOR ] [ OPTIONS ( option 'value' [, ... ] ) ]
CREATE FOREIGN DATA WRAPPER creates a new foreign-data wrapper. The user who defines a foreign-data wrapper becomes its owner.
The foreign-data wrapper name must be unique within the database.
Only superusers can create foreign-data wrappers.
The name of the foreign-data wrapper to be created.
valfunction is the name
of a previously registered function that will be called to
check the generic options given to the foreign-data
wrapper, as well as to foreign servers and user mappings
using the foreign-data wrapper. If no validator function or
NO VALIDATOR is specified, then
options will not be checked at creation time. (Foreign-data
wrappers will possibly ignore or reject invalid option
specifications at run time, depending on the
implementation.) The validator function must take two
arguments: one of type text, which
will contain the array of options as stored in the system
catalogs, and one of type oid, which
will be the OID of the system catalog containing the
options. The return type is ignored; the function should
indicate invalid options using the
This clause specifies options for the new foreign-data wrapper. The allowed option names and values are specific to each foreign data wrapper and are validated using the foreign-data wrapper library. Option names must be unique.
At the moment, the foreign-data wrapper functionality is very rudimentary. The purpose of foreign-data wrappers, foreign servers, and user mappings is to store this information in a standard way so that it can be queried by interested applications. One such application is dblink; see Section F.8. The functionality to actually query external data through a foreign-data wrapper library does not exist yet.
There is currently one foreign-data wrapper validator function provided: postgresql_fdw_validator, which accepts options corresponding to libpq connection parameters.
Create a foreign-data wrapper dummy:
CREATE FOREIGN DATA WRAPPER dummy;
Create a foreign-data wrapper postgresql with validator function postgresql_fdw_validator:
CREATE FOREIGN DATA WRAPPER postgresql VALIDATOR postgresql_fdw_validator;
Create a foreign-data wrapper mywrapper with some options:
CREATE FOREIGN DATA WRAPPER mywrapper OPTIONS (debug 'true');
CREATE FOREIGN DATA WRAPPER conforms to ISO/IEC 9075-9 (SQL/MED), with the exception that the VALIDATOR clause is an extension and the clauses LIBRARY and LANGUAGE are not yet implemented in PostgreSQL.
Note, however, that the SQL/MED functionality as a whole is not yet conforming.
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