Defines a new procedural language.
CREATE [PROCEDURAL] LANGUAGE <name> CREATE [TRUSTED] [PROCEDURAL] LANGUAGE <name> HANDLER <call_handler> [VALIDATOR <valfunction>]
CREATE LANGUAGE registers a new procedural language with a HAWQ database. Subsequently, functions can be defined in this new language. You must be a superuser to register a new language.
When you register a new procedural language, you effectively associate 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 HAWQ 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.
There are two forms of the
CREATE LANGUAGE command. In the first form, the user specifies the name of the desired language and the HAWQ 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
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 This behavior simplifies loading of old dump files, which are likely to contain out-of-date information about language support functions.
plpgsqlis installed by default in HAWQ.
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 HAWQ as a function taking no arguments and returning the
language_handlertype, a placeholder type that is simply used to identify the function as a call handler.
pg_pltemplate. <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
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 procedural language packages included in the standard HAWQ distribution are:
PL/pgSQL- registered in all databases by default
HAWQ supports a language handler for
PL/R, but the
PL/R language package is not pre-installed with HAWQ.
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. 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.
Any shared library that implements a language must be located in the same
LD_LIBRARY_PATH location on all segment hosts in your HAWQ array.
The preferred way of creating any of the standard procedural languages in a database:
CREATE LANGUAGE plr; CREATE LANGUAGE plpythonu; CREATE LANGUAGE plperl;
For a language not known in the
CREATE FUNCTION plsample_call_handler() RETURNS language_handler AS '$libdir/plsample' LANGUAGE C; CREATE LANGUAGE plsample HANDLER plsample_call_handler;
CREATE LANGUAGE is a HAWQ extension.