xenial (7) CREATE_LANGUAGE.7.gz
NAME
CREATE_LANGUAGE - define a new procedural language
SYNOPSIS
CREATE [ OR REPLACE ] [ PROCEDURAL ] LANGUAGE name
CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE name
HANDLER call_handler [ INLINE inline_handler ] [ VALIDATOR valfunction ]
DESCRIPTION
CREATE LANGUAGE registers a new procedural language with a PostgreSQL database. Subsequently, functions
and trigger procedures can be defined in this new language.
Note
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 53, 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dump files, which are likely to contain out-of-date information about language support functions.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.
PARAMETERS
TRUSTED
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.
PROCEDURAL
This is a noise word.
name
The name of the new procedural language. 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'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 inline_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.
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 Section 49.28, “pg_language”, 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, 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 language_handler.
EXAMPLES
The preferred way of creating any of the standard procedural languages is just:
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
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(7), REVOKE(7), createlang(1), droplang(1)