CREATE FUNCTION - Defines a new function
SYNOPSIS
CREATE FUNCTION name ( [ ftype [, ...] ] )
RETURNS rtype
AS definition
LANGUAGE 'langname'
[ WITH ( attribute [, ...] ) ]
CREATE FUNCTION name ( [ ftype [, ...] ] )
RETURNS rtype
AS obj_file , link_symbol
LANGUAGE 'langname'
[ WITH ( attribute [, ...] ) ]
INPUTS
name The name of a function to create.
ftype The data type(s) of the function's arguments, if
any. The input types may be base or complex types,
or opaque. Opaque indicates that the function
accepts arguments of a non-SQL type such as char *.
rtype The return data type. The output type may be spec
ified 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.
attribute
An optional piece of information about the func
tion, used for optimization. See below for details.
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.
obj_file , link_symbol
This form of the AS clause is used for dynamically
linked, C language functions when the function name
in the C language source code is not the same as
the name of the SQL function. The string obj_file
is the name of the file containing the dynamically
loadable object, and link_symbol is the object's
link symbol, that is the name of the function in
the C language source code.
langname
May be 'sql', 'C', 'internal', or 'plname', where
'plname' is the name of a created procedural
for details.
OUTPUTS
CREATE This is returned if the command completes success
fully.
DESCRIPTION
CREATE FUNCTION allows a Postgres user to register a func
tion with the database. Subsequently, this user is consid
ered the owner of the function.
FUNCTION ATTRIBUTES
The following items may appear in the WITH clause:
iscachable
Iscachable indicates that the function always
returns the same result when given the same argu
ment values (i.e., it does not do database lookups
or otherwise use information not directly present
in its parameter list). The optimizer uses
iscachable to know whether it is safe to pre-evalu
ate a call of the function.
isstrict
isstrict indicates that the function always returns
NULL whenever any of its arguments are NULL. If
this attribute is specified, the function is not
executed when there are NULL arguments; instead a
NULL result is assumed automatically. When
isstrict is not specified, the function will be
called for NULL inputs. It is then the function
author's responsibility to check for NULLs if nec
essary and respond appropriately.
NOTES
Refer to the chapter in the PostgreSQL Programmer's Guide
on the topic of extending Postgres via functions for fur
ther information on writing external functions.
Use DROP FUNCTION to remove user-defined functions.
The full SQL92 type syntax is allowed for input arguments
and return value. However, some details of the type speci
fication (e.g., the precision field for numeric types) are
the responsibility of the underlying function implementa
tion and are silently swallowed (i.e., not recognized or
enforced) by the CREATE FUNCTION command.
Postgres allows function "overloading"; that is, the same
name can be used for several different functions so long
be used with caution for internal and C-language func
tions, 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.
Similarly, when overloading SQL function names with multi
ple C-language functions, give each C-language instance of
the function a distinct name, then use the alternative
form of the AS clause in the CREATE FUNCTION syntax to
select the appropriate C-language implementation of each
overloaded SQL function.
USAGE
To create a simple SQL function:
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 rou
tine 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 boolean
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))
);
This example creates a function that does type conversion
type point. The function is implemented by a dynamically
loaded object that was compiled from C source. For Post
gres to find a type conversion function automatically, the
sql function has to have the same name as the return type,
and so overloading is unavoidable. The function name is
overloaded by using the second form of the AS clause in
the SQL definition:
CREATE FUNCTION point(complex) RETURNS point
AS '/home/bernie/pgsql/lib/complex.so', 'complex_to_point'
LANGUAGE 'c';
The C declaration of the function is:
Point * complex_to_point (Complex *z)
{
Point *p;
p = (Point *) palloc(sizeof(Point));
p->x = z->x;
p->y = z->y;
return p;
}
COMPATIBILITY
SQL92
CREATE FUNCTION is a Postgres language extension.
SQL/PSM
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 eventu
ally become a standard.
SQL/PSM CREATE FUNCTION has the following syntax:
CREATE FUNCTION name
( [ [ IN | OUT | INOUT ] type [, ...] ] )
RETURNS rtype
LANGUAGE 'langname'
ESPECIFIC routine
SQL-statement
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