CREATE FOREIGN DATA WRAPPER
Synopsis
CREATE FOREIGN DATA WRAPPERname [ HANDLERhandler_function | NO HANDLER ] [ VALIDATORvalidator_function | NO VALIDATOR ] [ OPTIONS (option 'value' [, ... ] ) ]
Description
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.
Parameters
- name
The name of the foreign-data wrapper to be created.
- HANDLERhandler_function
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 befdw_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.
- VALIDATORvalidator_function
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, user mappings and foreign tables using the foreign-data wrapper. If no validator function orNO 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 typetext[], which will contain the array of options as stored in the system catalogs, and one of typeoid, 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.- OPTIONS (option 'value' [, ... ] )
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.
Notes
PostgreSQL's foreign-data functionality is still under active development. Optimization of queries is primitive (and mostly left to the wrapper, too). Thus, there is considerable room for future performance improvements.
Examples
Create a useless foreign-data wrapperdummy:
CREATE FOREIGN DATA WRAPPER dummy;
Create a foreign-data wrapperfile with handler functionfile_fdw_handler:
CREATE FOREIGN DATA WRAPPER file HANDLER file_fdw_handler;
Create a foreign-data wrappermywrapper with some options:
CREATE FOREIGN DATA WRAPPER mywrapper OPTIONS (debug 'true');
Compatibility
CREATE FOREIGN DATA WRAPPER conforms to ISO/IEC 9075-9 (SQL/MED), with the exception that theHANDLER andVALIDATOR clauses are extensions and the standard clausesLIBRARY andLANGUAGE are not implemented inPostgreSQL.
Note, however, that the SQL/MED functionality as a whole is not yet conforming.