Using CREATE LANGUAGE, a PostgreSQL user can register a new procedural language with a PostgreSQL database. Subsequently, functions and trigger procedures can be defined in this new language. The user must have the PostgreSQL superuser privilege to register a new language.
CREATE LANGUAGE effectively associates the language name with a call handler that is responsible for executing functions written in the language. Refer to the Programmer's Guide for more information about language call handlers.
Note that procedural languages are local to individual databases. To make a language available in all databases by default, it should be installed into the template1 database.
TRUSTED specifies that the call handler for the language is safe, that is, it does not offer an unprivileged user any functionality to bypass access restrictions. If this keyword 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 language name is case insensitive. A procedural language cannot override one of the built-in languages of PostgreSQL.
For backward compatibility, the name may be enclosed by single quotes.
call_handler is the name of a previously registered function that will be called to execute the procedural language 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 opaque type, a placeholder for unspecified or undefined types.
This command normally should not be executed directly by users. For the procedural languages supplied in the PostgreSQL distribution, the createlang script should be used, which will also install the correct call handler. (createlang will call CREATE LANGUAGE internally.)
Use the CREATE FUNCTION command to create a new function.
The system catalog pg_language records information about the currently installed procedural languages.
Table "pg_language" Attribute | Type | Modifier ---------------+---------+---------- lanname | name | lanispl | boolean | lanpltrusted | boolean | lanplcallfoid | oid | lancompiler | text | lanname | lanispl | lanpltrusted | lanplcallfoid | lancompiler -------------+---------+--------------+---------------+------------- internal | f | f | 0 | n/a c | f | f | 0 | /bin/cc sql | f | t | 0 | postgres
At present, the definition of a procedural language cannot be changed once it has been created.
To be able to use a procedural language, a user must be granted the USAGE privilege. The createlang program automatically grants permissions to everyone if the language is known to be trusted.
The following two commands executed in sequence will register a new procedural language and the associated call handler.
CREATE FUNCTION plsample_call_handler () RETURNS opaque AS '$libdir/plsample' LANGUAGE C; CREATE LANGUAGE plsample HANDLER plsample_call_handler;