CREATE LANGUAGE — define a new procedural language
CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGEnameHANDLERcall_handler[ INLINEinline_handler] [ VALIDATORvalfunction] CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGEname
CREATE LANGUAGE registers a new
procedural language with a LightDB
database. Subsequently, functions and procedures can be
defined in this new language.
CREATE LANGUAGE effectively associates the
language name with handler function(s) that are responsible for executing
functions written in the language. Refer to Chapter 55
for more information about language handlers.
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 command,
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.
One must have the LightDB superuser privilege to register a new language or change an existing language's parameters. However, once the language is created it is valid to assign ownership of it to a non-superuser, who may then drop it, change its permissions, rename it, or assign it to a new owner. (Do not, however, assign ownership of the underlying C functions to a non-superuser; that would create a privilege escalation path for that user.)
The form of CREATE LANGUAGE that does not supply
any handler function is obsolete. For backwards compatibility with
old dump files, it is interpreted as CREATE EXTENSION.
That will work if the language has been packaged into an extension of
the same name, which is the conventional way to set up procedural
languages.
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
LightDB 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 LightDB 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.
Use DROP LANGUAGE to drop procedural languages.
The system catalog pg_language (see Section 51.30) records information about the
currently installed languages. Also, the ltsql
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.
A minimal sequence for creating a new procedural language is:
CREATE FUNCTION plsample_call_handler() RETURNS language_handler
AS '$libdir/plsample'
LANGUAGE C;
CREATE LANGUAGE plsample
HANDLER plsample_call_handler;
Typically that would be written in an extension's creation script, and users would do this to install the extension:
CREATE EXTENSION plsample;
CREATE LANGUAGE is a
LightDB extension.