Ubuntu Manpage: CREATE_LANGUAGE - define a new procedural language

Provided by: postgresql-client-9.3_9.3.24-0ubuntu0.14.04_amd64

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 51, 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behavior simplifies loading of old dump files, which are likely to contain out-of-date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 47.28, “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.