NAME
CREATE LANGUAGE - define a new procedural language
SYNOPSIS
CREATE [ PROCEDURAL ] LANGUAGE name
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
trigger procedures can be defined in this 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 in the documentation for more information about
language call 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dump files, which are likely to contain out-of-date information about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.
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 key word 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.
name The name of the new procedural language. The language name is
case insensitive. The name must be unique among the languages in
the database.
For backward compatibility, the name can 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 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.
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 ereport() function. The return value of
the function is ignored.
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.
NOTES
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 in the documentation) records
information about the currently installed languages. Also, createlang
has an option to list the installed languages.
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
desired.
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 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
language_handler.
EXAMPLES
The preferred way of creating any of the standard procedural languages
is just:
CREATE LANGUAGE plpgsql;
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
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_function(7)], DROP LANGUAGE [drop_language(7)], GRANT
[grant(7)], REVOKE [revoke(7)], createlang [createlang(1)], droplang
[droplang(1)]