CREATE FOREIGN DATA WRAPPER

CREATE FOREIGN DATA WRAPPER
Prev	Up	SQL Commands	Home	Next

CREATE FOREIGN DATA WRAPPER — define a new foreign-data wrapper

Synopsis

+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 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 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 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. +

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. +