CREATE FOREIGN DATA WRAPPER
CREATE FOREIGN DATA WRAPPER
7
SQL - Language Statements
CREATE FOREIGN DATA WRAPPER
define a new foreign-data wrapper
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.
See Also