CREATE LANGUAGE - define a new procedural language
CREATE [ OR REPLACE ] [ PROCEDURAL ] LANGUAGE
nameCREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE
inline_handler] [ VALIDATOR
registers a new
procedural language with a
database. Subsequently, functions and procedures can be
defined in this new language.
9.1, most procedural
languages have been made into
, and should
therefore be installed with
. Direct use of
should now be confined to
extension installation scripts. If you have a
language in your database, perhaps as a result of an upgrade,
you can convert it to an extension using
effectively associates the
language name with handler function(s) that are responsible for executing
functions written in the language. Refer to
for more information about language handlers.
There are two forms of the
In the first form, the user supplies just the name of the desired
language, and the
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
, but this approach is considered obsolescent.
When the server finds an entry in the
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old dump files, which are likely to contain out-of-date information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
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
catalog and is marked
as allowed to be created by database owners (
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
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
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.
case is mainly meant to be used to
ensure that the language exists. If the language has a
will not actually change anything about an existing definition, except in
the unusual case where the
has been modified since the language was created.
TRUSTEDspecifies 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 name must be unique among the languages in the database.
For backward compatibility, the name can be enclosed by single quotes.
call_handleris 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_handlertype, a placeholder type that is simply used to identify the function as a call handler.
inline_handleris 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_handlerfunction is specified, the language does not support anonymous code blocks. The handler function must take one argument of type
internal, which will be the
DOcommand's internal representation, and it will typically return
void. The return value of the handler is ignored.
valfunctionis 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 ignored.
option and the support function name(s) are
ignored if the server has an entry for the specified language
Use DROP LANGUAGE to drop procedural languages.
The system catalog
) records information about the
currently installed languages. Also, the
lists the installed languages.
To create functions in a procedural language, a user must have the
privilege for the language. By default,
is granted to
for trusted languages. This can be revoked if desired.
Procedural languages are local to individual databases.
However, a language can be installed into the
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
. 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
failing, if the
shared library that implements the language is not available in
versions before 7.3, it was
necessary to declare handler functions as returning the placeholder
, rather than
To support loading
of old dump files,
will accept a function
declared as returning
, 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 is just:
CREATE LANGUAGE plperl;
For a language not known in the
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;