CREATE FOREIGN DATA WRAPPER name
[ HANDLER handler_function | NO HANDLER ]
[ VALIDATOR validator_function | 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.
handler_function is the name of a previously registered function that will be called to retrieve the execution functions for foreign tables. The handler function must take no arguments, and its return type must be fdw_handler.
It is possible to create a foreign-data wrapper with no handler function, but foreign tables using such a wrapper can only be declared, not accessed.
validator_function 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 options for 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 report invalid options using
the ereport(ERROR)
function.
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's validator function. Option names must be unique.
At the moment, the foreign-data wrapper functionality is rudimentary. There is no support for updating a foreign table, and optimization of queries is primitive (and mostly left to the wrapper, too).
There is one built-in foreign-data wrapper validator function provided: postgresql_fdw_validator, which accepts options corresponding to libpq connection parameters.
Create a useless foreign-data wrapper dummy:
CREATE FOREIGN DATA WRAPPER dummy;
Create a foreign-data wrapper file with handler function file_fdw_handler:
CREATE FOREIGN DATA WRAPPER file HANDLER file_fdw_handler;
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 HANDLER and VALIDATOR clauses are extensions and the standard clauses LIBRARY and LANGUAGE are not implemented in PostgreSQL.
Note, however, that the SQL/MED functionality as a whole is not yet conforming.