CREATE
LANGUAGE(7) SQL Commands CREATE LANGUAGE(7)
NAME
CREATE LANGUAGE - define a new procedural language
SYNOPSIS
CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE langname
HANDLER call_handler [ VALIDATOR valfunction ]
DESCRIPTION
Using CREATE LANGUAGE, a PostgreSQL user can register a new procedural language with a PostgreSQL database. Subsequently, functions and
trigger procedures can be defined in this new language. The user must have the PostgreSQL superuser privilege to register a new language.
CREATE LANGUAGE effectively associates the language name with a call handler that is responsible for executing functions written in the
language. Refer to the Programmer's Guide for more information about language call handlers.
Note that procedural languages are local to individual databases. To make a language available in all databases by default, it should be
installed into the template1 database.
PARAMETERS
TRUSTED
TRUSTED specifies that the call handler for the language is safe, that is, it does not offer an unprivileged user any functionality
to bypass access restrictions. If this keyword is omitted when registering the language, only users with the PostgreSQL superuser
privilege can use this language to create new functions.
PROCEDURAL
This is a noise word.
langname
The name of the new procedural language. The language name is case insensitive. A procedural language cannot override one of the
built-in languages of PostgreSQL.
For backward compatibility, the name may be enclosed by single quotes.
HANDLER call_handler
call_handler is the name of a previously registered function that will be called to execute the procedural language functions. The
call handler for a procedural language must be written in a compiled language such as C with version 1 call convention and regis-
tered with PostgreSQL as a function taking no arguments and returning the language_handler type, a placeholder type that is simply
used to identify the function as a call handler.
VALIDATOR valfunction
valfunction is the name of a previously registered function that will be called when a new function in the language is created, to
validate the new function. If no validator function is specified, then a new function will not be checked when it is created. The
validator function must take one argument of type oid, which will be the OID of the to-be-created function, and will typically
return void.
A validator function would typically inspect the function body for syntactical correctness, but it can also look at other properties
of the function, for example if the language cannot handle certain argument types. To signal an error, the validator function should
use the elog() function. The return value of the function is ignored.
DIAGNOSTICS
CREATE LANGUAGE
This message is returned if the language is successfully created.
ERROR: PL handler function funcname() doesn't exist
This error is returned if the function funcname() is not found.
NOTES
This command normally should not be executed directly by users. For the procedural languages supplied in the PostgreSQL distribution, the
createlang(1) script should be used, which will also install the correct call handler. (createlang will call CREATE LANGUAGE internally.)
In PostgreSQL versions before 7.3, it was necessary to declare handler functions as returning the placeholder type opaque, rather than lan-
guage_handler. To support loading of old dump files, CREATE LANGUAGE will accept a function declared as returning opaque, but it will
issue a NOTICE and change the function's declared return type to language_handler.
Use the CREATE FUNCTION [create_function(7)] command to create a new function.
Use DROP LANGUAGE [drop_language(7)], or better yet the droplang(1) script, to drop procedural languages.
The system catalog pg_language records information about the currently installed procedural languages.
Table "pg_language"
Attribute | Type | Modifier
---------------+-----------+----------
lanname | name |
lanispl | boolean |
lanpltrusted | boolean |
lanplcallfoid | oid |
lanvalidator | oid |
lanacl | aclitem[] |
lanname | lanispl | lanpltrusted | lanplcallfoid | lanvalidator | lanacl
-------------+---------+--------------+---------------+--------------+--------
internal | f | f | 0 | 2246 |
c | f | f | 0 | 2247 |
sql | f | t | 0 | 2248 | {=U}
At present, with the exception of the permissions, the definition of a procedural language cannot be changed once it has been created.
To be able to use a procedural language, a user must be granted the USAGE privilege. The createlang program automatically grants permis-
sions to everyone if the language is known to be trusted.
EXAMPLES
The following two commands executed in sequence will register a new procedural language and the associated call handler.
CREATE FUNCTION plsample_call_handler () RETURNS language_handler
AS '$libdir/plsample'
LANGUAGE C;
CREATE LANGUAGE plsample
HANDLER plsample_call_handler;
COMPATIBILITY
CREATE LANGUAGE is a PostgreSQL extension.
HISTORY
The CREATE LANGUAGE command first appeared in PostgreSQL 6.3.
SEE ALSO
createlang(1), CREATE FUNCTION [create_function(7)], droplang(1), DROP LANGUAGE [drop_language(l)], GRANT [grant(l)], REVOKE [revoke(l)],
PostgreSQL Programmer's Guide
SQL - Language Statements 2002-11-22 CREATE LANGUAGE(7)