PostgreSQL 7.4 Documentation
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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 Section 33.3 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 43.18) records information about the currently installed languages. Also `createlang` has an option to list the installed languages.

The definition of a procedural language cannot be changed once it has been created, with the exception of the privileges.

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.

## See Also

ALTER LANGUAGE, CREATE FUNCTION, DROP LANGUAGE, GRANT, REVOKE, createlang, droplang

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