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CREATE LANGUAGE

Name

CREATE LANGUAGE -- define a new procedural language

Synopsis

CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE name
    HANDLER call_handler [ VALIDATOR valfunction ]

Description

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 Chapter 34 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.

Parameters

TRUSTED

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 key word is omitted when registering the language, only users with the PostgreSQL superuser privilege can use this language to create new functions.

PROCEDURAL

This is a noise word.

name

The name of the new procedural language. The language name is case insensitive. The name must be unique among the languages in the database.

For backward compatibility, the name may be enclosed by single quotes.

HANDLER call_handler

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 language_handler type, a placeholder type that is simply used to identify the function as a call handler.

VALIDATOR valfunction

valfunction 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.

Notes

This command normally should not be executed directly by users. For the procedural languages supplied in the PostgreSQL distribution, the createlang program should be used, which will also install the correct call handler. (createlang will call CREATE LANGUAGE internally.)

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.

Use the CREATE FUNCTION command to create a new function.

Use DROP LANGUAGE, or better yet the droplang program, to drop procedural languages.

The system catalog pg_language (see Section 41.18) records information about the currently installed languages. Also createlang has an option to list the installed languages.

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.

Examples

The following two commands executed in sequence will register a new procedural language and the associated call handler.

CREATE FUNCTION plsample_call_handler() RETURNS language_handler
    AS '$libdir/plsample'
    LANGUAGE C;
CREATE LANGUAGE plsample
    HANDLER plsample_call_handler;

Compatibility

CREATE LANGUAGE is a PostgreSQL extension.

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