CREATE LANGUAGE — define a new procedural language
CREATE [ OR REPLACE ] [ PROCEDURAL ] LANGUAGEnameCREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGEnameHANDLERcall_handler[ INLINEinline_handler] [ VALIDATORvalfunction]
CREATE LANGUAGE registers a new
procedural language with a PostgreSQL
database. Subsequently, functions and 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
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 56
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old dump files, which are likely to contain out-of-date information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.
TRUSTEDTRUSTED 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.
PROCEDURALThis is a noise word.
nameThe 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_handlercall_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_handlerinline_handler is the
name of a previously registered function that will be called
to execute an anonymous code block
(DO 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 valfunctionvalfunction 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.
Use DROP LANGUAGE to drop procedural languages.
The system catalog pg_language (see Section 52.29) records information about the
currently installed languages. Also, the psql
command \dL lists 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.
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;
CREATE LANGUAGE is a
PostgreSQL extension.