CREATE LANGUAGE

CREATE LANGUAGE

7

SQL - Language Statements

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

Description {#sql-createlanguage-description}
===========

`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 [???](#plhandler) 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is obsolete.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.

Parameters {#sql-createlanguage-parameters}
==========

`TRUSTED`

:   `TRUSTED` 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 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 name must be unique
    among the languages in the database.

`HANDLER` call\_handler

:   call\_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 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.

`INLINE` inline\_handler

:   inline\_handler is the name of a previously registered function that
    will be called to execute an anonymous code block ([`DO`](#sql-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` 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 {#sql-createlanguage-notes}
=====

Use [`DROP LANGUAGE`](#sql-droplanguage) to drop procedural languages.

The system catalog `pg_language` (see [???](#catalog-pg-language))
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.

Examples {#sql-createlanguage-examples}
========

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;

Compatibility {#sql-createlanguage-compat}
=============

`CREATE LANGUAGE` is a PostgreSQL extension.

See Also
========
