CREATE LANGUAGE

CREATE LANGUAGE

Defines a new procedural language.

Synopsis

CREATE [PROCEDURAL] LANGUAGE name

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

Description

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

Superusers can register a new language with a Greenplum database. A database owner can also register within that database any language listed in the pg_pltemplate catalog in which the tmpldbacreate field is true. The default configuration allows only trusted languages to be registered by database owners. The creator of a language becomes its owner and can later drop it, rename it, or assign ownership to a new user.

CREATE LANGUAGE effectively associates the language name with a call handler that is responsible for executing functions written in that language. For a function written in a procedural language (a language other than C or SQL), the database server has no built-in knowledge about how to interpret the function's source code. The task is passed to a special handler that knows the details of the language. The handler could either do all the work of parsing, syntax analysis, execution, and so on or it could serve as a bridge between Greenplum Database and an existing implementation of a programming language. The handler itself is a C language function compiled into a shared object and loaded on demand, just like any other C function. Therese procedural language packages are included in the standard Greenplum Database distribution: PL/pgSQL, PL/Perl, and PL/Python. Language handlers have also been added for PL/Java and PL/R, but those languages are not pre-installed with Greenplum Database. See the topic on Procedural Languages in the PostgreSQL documentation for more information on developing functions using these procedural languages.

The PL/Perl, PL/Java, and PL/R libraries require the correct versions of Perl, Java, and R to be installed, respectively.

There are two forms of the CREATE LANGUAGE command. In the first form, the user specifies the name of the desired language and the Greenplum Database server uses the pg_pltemplate system catalog to determine the correct parameters. In the second form, the user specifies the language parameters as well as the language name. You can use the second form to create a language that is not defined in pg_pltemplate.

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
Ignored if the server has an entry for the specified language name in pg_pltemplate. Specifies that the call handler for the language is safe and 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 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. Built-in support is included for plpgsql, plperl, plpython, plpythonu, and plr. The languages plpgsql (PL/pgSQL) and plpythonu (PL/Python) are installed by default in Greenplum Database.
HANDLER call_handler
Ignored if the server has an entry for the specified language name in pg_pltemplate. 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 Greenplum Database 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
The name of a previously registered function that is called to execute an anonymous code block in this language that is created with the DO command. If an inline_handler function is not specified, the language does not support anonymous code blocks. The handler function must take one argument of type internal, which is the DO command internal representation. The function typically return void. The return value of the handler is ignored.
VALIDATOR valfunction
Ignored if the server has an entry for the specified language name in pg_pltemplate. 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 Greenplum Database 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.

Notes

The PL/pgSQL language is already registered in all databases by default. The PL/Python language extension is installed but not registered.

The system catalog pg_language records information about the currently 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 (everyone) for trusted languages. This may be revoked if desired.

Procedural languages are local to individual databases. You create and drop languages for individual 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.

Any shared library that implements a language must be located in the same LD_LIBRARY_PATH location on all segment hosts in your Greenplum Database array.

Examples

The preferred way of creating any of the standard procedural languages:

CREATE LANGUAGE plpgsql;
CREATE LANGUAGE plr;

For a language not known in the pg_pltemplate catalog:

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 Greenplum Database extension.