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.\" Title: CREATE LANGUAGE
.\" Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\" Date: 2017-11-06
.\" Manual: PostgreSQL 9.2.24 Documentation
.\" Source: PostgreSQL 9.2.24
.\" Language: English
.\"
.TH "CREATE LANGUAGE" "7" "2017-11-06" "PostgreSQL 9.2.24" "PostgreSQL 9.2.24 Documentation"
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.SH "NAME"
CREATE_LANGUAGE \- define a new procedural language
.\" CREATE LANGUAGE
.SH "SYNOPSIS"
.sp
.nf
CREATE [ OR REPLACE ] [ PROCEDURAL ] LANGUAGE \fIname\fR
CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE \fIname\fR
HANDLER \fIcall_handler\fR [ INLINE \fIinline_handler\fR ] [ VALIDATOR \fIvalfunction\fR ]
.fi
.SH "DESCRIPTION"
.PP
\fBCREATE LANGUAGE\fR
registers a new procedural language with a
PostgreSQL
database\&. Subsequently, functions and trigger procedures can be defined in this new language\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
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.br
.ps +1
\fBNote\fR
.ps -1
.br
.PP
As of
PostgreSQL
9\&.1, most procedural languages have been made into
\(lqextensions\(rq, and should therefore be installed with
CREATE EXTENSION (\fBCREATE_EXTENSION\fR(7))
not
\fBCREATE LANGUAGE\fR\&. Direct use of
\fBCREATE LANGUAGE\fR
should now be confined to extension installation scripts\&. If you have a
\(lqbare\(rq
language in your database, perhaps as a result of an upgrade, you can convert it to an extension using
CREATE EXTENSION \fIlangname\fR FROM unpackaged\&.
.sp .5v
.RE
.PP
\fBCREATE LANGUAGE\fR
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\&.
.PP
There are two forms of the
\fBCREATE LANGUAGE\fR
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\&.
.PP
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\&.
.PP
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\&.
.PP
\fBCREATE OR REPLACE LANGUAGE\fR
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\*(Aqs 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\&.
.SH "PARAMETERS"
.PP
TRUSTED
.RS 4
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\&.
.RE
.PP
PROCEDURAL
.RS 4
This is a noise word\&.
.RE
.PP
\fIname\fR
.RS 4
The name of the new procedural language\&. The name must be unique among the languages in the database\&.
.sp
For backward compatibility, the name can be enclosed by single quotes\&.
.RE
.PP
HANDLER \fIcall_handler\fR
.RS 4
\fIcall_handler\fR
is the name of a previously registered function that will be called to execute the procedural language\*(Aqs 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\&.
.RE
.PP
INLINE \fIinline_handler\fR
.RS 4
\fIinline_handler\fR
is the name of a previously registered function that will be called to execute an anonymous code block (\fBDO\fR(7)
command) in this language\&. If no
\fIinline_handler\fR
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
\fBDO\fR
command\*(Aqs internal representation, and it will typically return
void\&. The return value of the handler is ignored\&.
.RE
.PP
VALIDATOR \fIvalfunction\fR
.RS 4
\fIvalfunction\fR
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\&.
.sp
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
\fBereport()\fR
function\&. The return value of the function is ignored\&.
.RE
.PP
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\&.
.SH "NOTES"
.PP
The
\fBcreatelang\fR(1)
program is a simple wrapper around the
\fBCREATE LANGUAGE\fR
command\&. It eases installation of procedural languages from the shell command line\&.
.PP
Use
DROP LANGUAGE (\fBDROP_LANGUAGE\fR(7)), or better yet the
\fBdroplang\fR(1)
program, to drop procedural languages\&.
.PP
The system catalog
pg_language
(see
Section 45.27, \(lqpg_language\(rq, in the documentation) records information about the currently installed languages\&. Also,
\fBcreatelang\fR
has an option to list the installed languages\&.
.PP
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\&.
.PP
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\&.
.PP
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
\fBCREATE LANGUAGE\fR
failing, if the shared library that implements the language is not available in the installation\&.)
.PP
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,
\fBCREATE LANGUAGE\fR
will accept a function declared as returning
opaque, but it will issue a notice and change the function\*(Aqs declared return type to
language_handler\&.
.SH "EXAMPLES"
.PP
The preferred way of creating any of the standard procedural languages is just:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE LANGUAGE plperl;
.fi
.if n \{\
.RE
.\}
.PP
For a language not known in the
pg_pltemplate
catalog, a sequence such as this is needed:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE FUNCTION plsample_call_handler() RETURNS language_handler
AS \*(Aq$libdir/plsample\*(Aq
LANGUAGE C;
CREATE LANGUAGE plsample
HANDLER plsample_call_handler;
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
\fBCREATE LANGUAGE\fR
is a
PostgreSQL
extension\&.
.SH "SEE ALSO"
ALTER LANGUAGE (\fBALTER_LANGUAGE\fR(7)), CREATE FUNCTION (\fBCREATE_FUNCTION\fR(7)), DROP LANGUAGE (\fBDROP_LANGUAGE\fR(7)), \fBGRANT\fR(7), \fBREVOKE\fR(7), \fBcreatelang\fR(1), \fBdroplang\fR(1)
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