CREATE FUNCTION name ( [ ftype [, ...] ] )
RETURNS rtype
AS definition
LANGUAGE 'langname'
The name of a function to create.
The data type of function arguments.
The return data type.
A string defining the function; the meaning depends on the language. It may be an internal function name, the path to an object file, an SQL query, or text in a procedural language.
may be 'C', 'sql', 'internal' or 'plname', where 'plname' is the name of a created procedural language. See CREATE LANGUAGE for details.
This is returned if the command completes successfully.
CREATE FUNCTION allows a Postgres user to register a function with a database. Subsequently, this user is treated as the owner of the function.
Refer to the chapter on functions in the PostgreSQL Programmer's Guide for further information.
Use DROP FUNCTION to drop user-defined functions.
Postgres allows function "overloading"; that is, the same name can be used for several different functions so long as they have distinct argument types. This facility must be used with caution for INTERNAL and C-language functions, however.
Two INTERNAL functions cannot have the same C name without causing errors at link time. To get around that, give them different C names (for example, use the argument types as part of the C names), then specify those names in the AS clause of CREATE FUNCTION. If the AS clause is left empty then CREATE FUNCTION assumes the C name of the function is the same as the SQL name.
For dynamically-loaded C functions, the SQL name of the function must be the same as the C function name, because the AS clause is used to give the path name of the object file containing the C code. In this situation it is best not to try to overload SQL function names. It might work to load a C function that has the same C name as an internal function or another dynamically-loaded function --- or it might not. On some platforms the dynamic loader may botch the load in interesting ways if there is a conflict of C function names. So, even if it works for you today, you might regret overloading names later when you try to run the code somewhere else.
To create a simple SQL function:
CREATE FUNCTION one() RETURNS int4
AS 'SELECT 1 AS RESULT'
LANGUAGE 'sql';
SELECT one() AS answer;
answer
------
1
To create a C function, calling a routine from a user-created shared library. This particular routine calculates a check digit and returns TRUE if the check digit in the function parameters is correct. It is intended for use in a CHECK contraint.
CREATE FUNCTION ean_checkdigit(bpchar, bpchar) RETURNS bool
AS '/usr1/proj/bray/sql/funcs.so' LANGUAGE 'c';
CREATE TABLE product (
id char(8) PRIMARY KEY,
eanprefix char(8) CHECK (eanprefix ~ '[0-9]{2}-[0-9]{5}')
REFERENCES brandname(ean_prefix),
eancode char(6) CHECK (eancode ~ '[0-9]{6}'),
CONSTRAINT ean CHECK (ean_checkdigit(eanprefix, eancode))
);
A C function cannot return a set of values.
CREATE FUNCTION is a Postgres language extension.
SQL/PSM CREATE FUNCTION has the following syntax:Note: PSM stands for Persistent Stored Modules. It is a procedural language and it was originally hoped that PSM would be ratified as an official standard by late 1996. As of mid-1998, this has not yet happened, but it is hoped that PSM will eventually become a standard.
CREATE FUNCTION name
( [ [ IN | OUT | INOUT ] etereable>eable> type [, ...] ] )
RETURNS rtype
LANGUAGE 'langname'
ESPECIFIC routine
SQL-statement