CREATE_FUNCTION (l)
Defines a new function
SYNOPSIS
CREATE FUNCTION name ( [ ftype [, ...] ] )
RETURNS rtype
AS definition
LANGUAGE 'langname'
name
The name of a function to create.
ftype
The data type of function arguments.
The input types may be base or complex types, or
opaque .
opaque indicates that the function
accepts arguments of an invalid type such as char *.
rtype
The return data type.
The output type may be specified as a base type, complex type,
setof type ,
or opaque.
The setof
modifier indicates that the function will return a set of items,
rather than a single item.
definition
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.
langname
may be 'C', 'sql',
'internal'
or 'plname ',
where 'plname'
is the name of a created procedural
language. See
create_language(l)
for details.
CREATE
This is returned if the command completes successfully.
DESCRIPTION
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 in
the PostgreSQL Programmer's Guide
on extending
Postgres via functions
for further information on writing external functions.
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.
A C function cannot return a set of values.
USAGE
CREATE FUNCTION one() RETURNS int4
AS 'SELECT 1 AS RESULT'
LANGUAGE 'sql';
SELECT one() AS answer;
answer
------
1
This example creates a C function by 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))
);
COMPATIBILITY
CREATE FUNCTION is
a Postgres language extension.
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.
SQL/PSM CREATE FUNCTION has the following syntax:
CREATE FUNCTION name
( [ [ IN | OUT | INOUT ] etereable>eable> type [, ...] ] )
RETURNS rtype
LANGUAGE 'langname'
ESPECIFIC routine
SQL-statement
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