CREATE LANGUAGE(7) SQL Commands CREATE LANGUAGE(7)
NAME
CREATE LANGUAGE - define a new procedural language
SYNOPSIS
CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE name
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 trig-
ger procedures can be defined in(1,8) 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(1,8) the lan-
guage. Refer to the section called ``User-Defined Functions'' in(1,8) the
documentation for more information about language call handlers.
Note that procedural languages are local to individual databases. To
make a language available in(1,8) 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 func-
tionality to bypass access(2,5) restrictions. If this key word is
omitted when registering the language, only users(1,5) with the Post-
greSQL superuser privilege can use this language to create new
functions.
PROCEDURAL
This is a noise word.
name The name of the new procedural language. The language name is
case insensitive. The name must be unique among the languages in(1,8)
the database.
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 func-
tions. The call handler for a procedural language must be writ-
ten in(1,8) a compiled language such as C with version(1,3,5) 1 call conven-
tion and registered 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 han-
dler.
VALIDATOR valfunction
valfunction is the name of a previously registered function that
will be called when a new function in(1,8) the language is created,
to validate the new function. If no validator function is spec-
ified, then a new function will not be checked when it is cre-
ated. 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(1,8,3 Search::Dict) at other prop-
erties of the function, for example if(3,n) the language cannot han-
dle certain argument types. To signal(2,7) an error(8,n), the validator
function should use the ereport() function. The return value of
the function is ignored.
NOTES
This command normally should not be executed directly by users. For
the procedural languages supplied in(1,8) the PostgreSQL distribution, the
createlang(1) program should be used, which will also install the cor-
rect 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(2,8) a function declared as returning opaque, but it will issue
a notice and change the function's declared return type to lan-
guage_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)
program, to drop procedural languages.
The system catalog pg_language (see the chapter called ``System Cata-
logs'' in(1,8) the documentation) records information about the currently
installed languages. Also createlang has an option to list the
installed languages.
The definition of a procedural language cannot be changed once it has
been created, with the exception of the privileges.
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(3,n) the language is known to be trusted.
EXAMPLES
The following two commands executed in(1,8) 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.
SEE ALSO
ALTER LANGUAGE [alter_language(7)], CREATE FUNCTION [create_func-
tion(l)], DROP LANGUAGE [drop_language(l)], GRANT [grant(l)], REVOKE
[revoke(l)], createlang(1), droplang(1)
SQL - Language Statements 2003-11-02 CREATE LANGUAGE(7)