Provided by: postgresql-client-9.1_9.1.3-2_i386
CREATE_LANGUAGE - define a new procedural language
CREATE [ OR REPLACE ] [ PROCEDURAL ] LANGUAGE name
CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE name
HANDLER call_handler [ INLINE inline_handler ] [ VALIDATOR valfunction ]
CREATE LANGUAGE registers a new procedural language with a PostgreSQL
database. Subsequently, functions and trigger procedures can be defined
in this new language.
As of PostgreSQL 9.1, most procedural languages have been made into
"extensions", and should therefore be installed with CREATE
EXTENSION (CREATE_EXTENSION(7)) not CREATE LANGUAGE. Direct use of
CREATE LANGUAGE should now be confined to extension installation
scripts. If you have a "bare" language in your database, perhaps as
a result of an upgrade, you can convert it to an extension using
CREATE EXTENSION langname FROM unpackaged.
CREATE LANGUAGE effectively associates the language name with handler
function(s) that are responsible for executing functions written in the
language. Refer to Chapter 49, Writing A Procedural Language Handler,
in the documentation for more information about language handlers.
There are two forms of the CREATE LANGUAGE command. In the first form,
the user supplies just the name of the desired language, and the
PostgreSQL server consults the pg_pltemplate system catalog to
determine the correct parameters. In the second form, the user supplies
the language parameters along with the language name. The second form
can be used to create a language that is not defined in pg_pltemplate,
but this approach is considered obsolescent.
When the server finds an entry in the pg_pltemplate catalog for the
given language name, it will use the catalog data even if the command
includes language parameters. This behavior simplifies loading of old
dump files, which are likely to contain out-of-date information about
language support functions.
Ordinarily, the user must have the PostgreSQL superuser privilege to
register a new language. However, the owner of a database can register
a new language within that database if the language is listed in the
pg_pltemplate catalog and is marked as allowed to be created by
database owners (tmpldbacreate is true). The default is that trusted
languages can be created by database owners, but this can be adjusted
by superusers by modifying the contents of pg_pltemplate. The creator
of a language becomes its owner and can later drop it, rename it, or
assign it to a new owner.
CREATE OR REPLACE LANGUAGE will either create a new language, or
replace an existing definition. If the language already exists, its
parameters are updated according to the values specified or taken from
pg_pltemplate, but the language's ownership and permissions settings do
not change, and any existing functions written in the language are
assumed to still be valid. In addition to the normal privilege
requirements for creating a language, the user must be superuser or
owner of the existing language. The REPLACE case is mainly meant to be
used to ensure that the language exists. If the language has a
pg_pltemplate entry then REPLACE will not actually change anything
about an existing definition, except in the unusual case where the
pg_pltemplate entry has been modified since the language was created.
TRUSTED specifies that the language does not grant access to data
that the user would not otherwise have. If this key word is omitted
when registering the language, only users with the PostgreSQL
superuser privilege can use this language to create new functions.
This is a noise word.
The name of the new procedural language. The language name is case
insensitive. The name must be unique among the languages in the
For backward compatibility, the name can be enclosed by single
call_handler is the name of a previously registered function that
will be called to execute the procedural language's functions. The
call handler for a procedural language must be written in a
compiled language such as C with version 1 call convention 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 handler.
inline_handler is the name of a previously registered function that
will be called to execute an anonymous code block (DO(7) command)
in this language. If no inline_handler function is specified, the
language does not support anonymous code blocks. The handler
function must take one argument of type internal, which will be the
DO command's internal representation, and it will typically return
void. The return value of the handler is ignored.
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
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 ereport() function. The return value of the function is
The TRUSTED option and the support function name(s) are ignored if the
server has an entry for the specified language name in pg_pltemplate.
The createlang(1) program is a simple wrapper around the CREATE
LANGUAGE command. It eases installation of procedural languages from
the shell command line.
Use DROP LANGUAGE (DROP_LANGUAGE(7)), or better yet the droplang(1)
program, to drop procedural languages.
The system catalog pg_language (see Section 45.27, "pg_language", in
the documentation) records information about the currently installed
languages. Also, createlang has an option to list the installed
To create functions in a procedural language, a user must have the
USAGE privilege for the language. By default, USAGE is granted to
PUBLIC (i.e., everyone) for trusted languages. This can be revoked if
Procedural languages are local to individual databases. However, a
language can be installed into the template1 database, which will cause
it to be available automatically in all subsequently-created databases.
The call handler function, the inline handler function (if any), and
the validator function (if any) must already exist if the server does
not have an entry for the language in pg_pltemplate. But when there is
an entry, the functions need not already exist; they will be
automatically defined if not present in the database. (This might
result in CREATE LANGUAGE failing, if the shared library that
implements the language is not available in the installation.)
In PostgreSQL versions before 7.3, it was necessary to declare handler
functions as returning the placeholder type opaque, rather than
language_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
The preferred way of creating any of the standard procedural languages
CREATE LANGUAGE plperl;
For a language not known in the pg_pltemplate catalog, a sequence such
as this is needed:
CREATE FUNCTION plsample_call_handler() RETURNS language_handler
CREATE LANGUAGE plsample
CREATE LANGUAGE is a PostgreSQL extension.
ALTER LANGUAGE (ALTER_LANGUAGE(7)), CREATE FUNCTION
(CREATE_FUNCTION(7)), DROP LANGUAGE (DROP_LANGUAGE(7)), GRANT(7),
REVOKE(7), createlang(1), droplang(1)