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CREATE LANGUAGE()		 SQL Commands		     CREATE LANGUAGE()



NAME
       CREATE LANGUAGE - define a new procedural language


SYNOPSIS
       CREATE [ PROCEDURAL ] LANGUAGE name
       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	 trig-
       ger  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 lan-
       guage. Refer to the documentation for more information  about  language
       call 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	 Post-
       greSQL  server  consults	 the pg_pltemplate system catalog to determine
       the correct parameters. In the second form, the user supplies the  lan-
       guage  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       dump files, which are likely to contain out-of-date  information	 about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.

PARAMETERS
       TRUSTED
	      TRUSTED  specifies  that	the  call  handler for the language is
	      safe, that is, it does not offer an unprivileged user any	 func-
	      tionality	 to  bypass  access  restrictions. If this key word is
	      omitted when registering the language, only users with the Post-
	      greSQL  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	 func-
	      tions.  The call handler for a procedural language must be writ-
	      ten in a compiled language such as C with version 1 call conven-
	      tion  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 spec-
	      ified,  then  a new function will not be checked when it is cre-
	      ated.  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 prop-
	      erties of the function, for example if the language cannot  han-
	      dle  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  LAN-
       GUAGE  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 the documentation) records informa-
       tion 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  PUB-
       LIC  (i.e.,  everyone)  for  trusted  languages. This may 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  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  can result in CREATE LANGUAGE failing, if the shared
       library that implements the language is not available in the  installa-
       tion.)

       In  PostgreSQL versions before 7.3, it was necessary to declare handler
       functions as returning the placeholder type opaque,  rather  than  lan-
       guage_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 lan-
       guage_handler.

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

       CREATE LANGUAGE plpgsql;


       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_func-
       tion(l)],  DROP	LANGUAGE  [drop_language(l)], GRANT [grant(l)], REVOKE
       [revoke(l)], createlang [createlang(1)], droplang [droplang(1)]



SQL - Language Statements	  2010-12-14		     CREATE LANGUAGE()
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