Name
CREATE FOREIGN DATA WRAPPER -- define a new foreign-data wrapperSynopsis
CREATE FOREIGN DATA WRAPPER name [ HANDLER handler_function | NO HANDLER ] [ VALIDATOR validator_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.
HANDLER
handler_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.
VALIDATOR
validator_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 theereport(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 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');
Compatibility
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.
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