CREATE FUNCTION() SQL Commands CREATE FUNCTION()NAME
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 specified as a
base type, complex type, setof type, or opaque. The setof modi‐
fier indicates that the function will return a set of items,
rather than a single item.
attribute
An optional piece of information about the function, used for
optimization. See below for details.
definition
A string defining the function; the meaning depends on the lan‐
guage. 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 dynami‐
cally loadable object, and link_symbol is the object's link sym‐
bol, 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 language. See CREATE LANGUAGE
[create_language(l)] for details.
OUTPUTS
CREATE This is returned if the command completes successfully.
DESCRIPTION
CREATE FUNCTION allows a Postgres user to register a function with the
database. Subsequently, this user is considered the owner of the func‐
tion.
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 argument 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-evaluate a call of the function.
isstrict
isstrict indicates that the function always returns NULL when‐
ever any of its arguments are NULL. If this attribute is speci‐
fied, the function is not executed when there are NULL argu‐
ments; 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 necessary and respond appropriately.
NOTES
Refer to the chapter in the PostgreSQL Programmer's Guide on the topic
of extending Postgres via functions for further 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 specification (e.g., the pre‐
cision field for numeric types) are the responsibility of the underly‐
ing function implementation and are silently swallowed (i.e., not rec‐
ognized 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 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.
Similarly, when overloading SQL function names with multiple 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-cre‐
ated shared library. This particular routine calculates a check digit
and returns TRUE if the check digit in the function parameters is cor‐
rect. 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 between the
user-defined type complex, and the internal type point. The function is
implemented by a dynamically loaded object that was compiled from C
source. For Postgres 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 proce‐
dural 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
SQL - Language Statements 29 March 2001 CREATE FUNCTION()