|CREATE LANGUAGE(7)||PostgreSQL 15.4 Documentation||CREATE LANGUAGE(7)|
CREATE_LANGUAGE - define a new procedural language
CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE name
HANDLER call_handler [ INLINE inline_handler ] [ VALIDATOR valfunction ] CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE name
CREATE LANGUAGE registers a new procedural language with a PostgreSQL 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 58 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 PostgreSQL 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The form of CREATE LANGUAGE that does not supply any handler function is obsolete.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.
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 53.29) 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.
A minimal sequence for creating a new procedural language is:
CREATE FUNCTION plsample_call_handler() RETURNS language_handler
LANGUAGE C; CREATE LANGUAGE plsample
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 PostgreSQL extension.