CREATE LANGUAGE(7)	PostgreSQL 9.2.24 Documentation	    CREATE LANGUAGE(7)



NAME
       CREATE_LANGUAGE - define a new procedural language

SYNOPSIS
       CREATE [ OR REPLACE ] [ PROCEDURAL ] LANGUAGE name
       CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE name
	   HANDLER call_handler [ INLINE inline_handler ] [ VALIDATOR valfunction ]

DESCRIPTION
       CREATE LANGUAGE registers a new procedural language with a PostgreSQL
       database. Subsequently, functions and trigger procedures can be defined
       in this new language.

	   Note
	   As of PostgreSQL 9.1, most procedural languages have been made into
	   "extensions", and should therefore be installed with CREATE
	   EXTENSION (CREATE_EXTENSION(7)) not CREATE LANGUAGE. Direct use of
	   CREATE LANGUAGE should now be confined to extension installation
	   scripts. If you have a "bare" language in your database, perhaps as
	   a result of an upgrade, you can convert it to an extension using
	   CREATE EXTENSION langname FROM unpackaged.

       CREATE LANGUAGE effectively associates the language name with handler
       function(s) that are responsible for executing functions written in the
       language. Refer to Chapter 49, Writing A Procedural Language Handler,
       in the documentation for more information about language handlers.

       There are two forms of the CREATE LANGUAGE command. In the first form,
       the user supplies just the name of the desired language, and the
       PostgreSQL server consults the pg_pltemplate system catalog to
       determine the correct parameters. In the second form, the user supplies
       the language parameters along with the language name. The second form
       can be used to create a language that is not defined in pg_pltemplate,
       but this approach is considered obsolescent.

       When the server finds an entry in the pg_pltemplate catalog for the
       given language name, it will use the catalog data even if the command
       includes language parameters. This behavior simplifies loading of old
       dump files, which are likely to contain out-of-date information about
       language support functions.

       Ordinarily, the user must have the PostgreSQL superuser privilege to
       register a new language. However, the owner of a database can register
       a new language within that database if the language is listed in the
       pg_pltemplate catalog and is marked as allowed to be created by
       database owners (tmpldbacreate is true). The default is that trusted
       languages can be created by database owners, but this can be adjusted
       by superusers by modifying the contents of pg_pltemplate. The creator
       of a language becomes its owner and can later drop it, rename it, or
       assign it to a new owner.

       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 values specified or taken from
       pg_pltemplate, 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. In addition to the normal privilege
       requirements for creating a language, the user must be superuser or
       owner of the existing language. The REPLACE case is mainly meant to be
       used to ensure that the language exists. If the language has a
       pg_pltemplate entry then REPLACE will not actually change anything
       about an existing definition, except in the unusual case where the
       pg_pltemplate entry has been modified since the language was created.

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.

	   For backward compatibility, the name can 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'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(7) 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.

       The TRUSTED option and the support function name(s) are ignored if the
       server has an entry for the specified language name in pg_pltemplate.

NOTES
       The createlang(1) program is a simple wrapper around the CREATE
       LANGUAGE command. It eases installation of procedural languages from
       the shell command line.

       Use DROP LANGUAGE (DROP_LANGUAGE(7)), or better yet the droplang(1)
       program, to drop procedural languages.

       The system catalog pg_language (see Section 45.27, "pg_language", in
       the documentation) records information about the currently installed
       languages. Also, createlang has an option to list 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.

       The call handler function, the inline handler function (if any), and
       the validator function (if any) must already exist if the server does
       not have an entry for the language in pg_pltemplate. But when there is
       an entry, the functions need not already exist; they will be
       automatically defined if not present in the database. (This might
       result in CREATE LANGUAGE failing, if the shared library that
       implements the language is not available in the installation.)

       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.

EXAMPLES
       The preferred way of creating any of the standard procedural languages
       is just:

	   CREATE LANGUAGE plperl;

       For a language not known in the pg_pltemplate catalog, a sequence such
       as this is needed:

	   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 (ALTER_LANGUAGE(7)), CREATE FUNCTION
       (CREATE_FUNCTION(7)), DROP LANGUAGE (DROP_LANGUAGE(7)), GRANT(7),
       REVOKE(7), createlang(1), droplang(1)



PostgreSQL 9.2.24		  2017-11-06		    CREATE LANGUAGE(7)