create_function
CREATE FUNCTION() SQL Commands CREATE FUNCTION()
NAME
CREATE FUNCTION - define a new function
SYNOPSIS
CREATE [ OR REPLACE ] FUNCTION name ( [ argtype [, ...] ] )
RETURNS rettype
{ LANGUAGE langname
| IMMUTABLE | STABLE | VOLATILE
| CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
| [EXTERNAL] SECURITY INVOKER | [EXTERNAL] SECURITY DEFINER
| AS ’definition’
| AS ’obj_file’, ’link_symbol’
} ...
[ WITH ( attribute [, ...] ) ]
DESCRIPTION
CREATE FUNCTION defines a new function. CREATE OR REPLACE FUNCTION
will either create a new function, or replace an existing definition.
If a schema name is included, then the function is created in the
specified schema. Otherwise it is created in the current schema. The
name of the new function must not match any existing function with the
same argument types in the same schema. However, functions of differ-
ent argument types may share a name (this is called overloading).
To update the definition of an existing function, use CREATE OR
REPLACE FUNCTION. It is not possible to change the name or argument
types of a function this way (if you tried, you’d just be creating a
new, distinct function). Also, CREATE OR REPLACE FUNCTION will not let
you change the return type of an existing function. To do that, you
must drop and recreate the function.
If you drop and then recreate a function, the new function is not the
same entity as the old; you will break existing rules, views, trig-
gers, etc. that referred to the old function. Use CREATE OR REPLACE
FUNCTION to change a function definition without breaking objects that
refer to the function.
The user that creates the function becomes the owner of the function.
PARAMETERS
name The name of a function to create.
argtype
The data type(s) of the function’s arguments (optionally
schema-qualified), if any. The argument types may be base, com-
plex, or domains, or copy the type of an existing column.
The type of a column is referenced by writing tablename.column-
name%TYPE; using this can sometimes help make a function inde-
pendent from changes to the definition of a table.
Depending on the implementation language it may also be allowed
to specify ‘‘pseudotypes’’ such as cstring. Pseudotypes indi-
cate that the actual argument type is either incompletely spec-
ified, or outside the set of ordinary SQL data types.
rettype
The return data type (optionally schema-qualified). The return
type may be a base type, complex type, or a domain, or may be
specified to copy the type of an existing column. See the
description under argtype above on how to reference the type of
an existing column.
Depending on the implementation language it may also be allowed
to specify ‘‘pseudotypes’’ such as cstring. The SETOF modifier
indicates that the function will return a set of items, rather
than a single item.
langname
The name of the language that the function is implemented in.
May be SQL, C, internal, or the name of a user-defined procedu-
ral language. (See also createlang [createlang(1)].) For back-
ward compatibility, the name may be enclosed by single quotes.
IMMUTABLE
STABLE
VOLATILE
These attributes inform the system whether it is safe to
replace multiple evaluations of the function with a single
evaluation, for run-time optimization. At most one choice
should be specified. If none of these appear, VOLATILE is the
default assumption.
IMMUTABLE indicates that the function always returns the same
result when given the same argument values; that is, it does
not do database lookups or otherwise use information not
directly present in its argument list. If this option is given,
any call of the function with all-constant arguments can be
immediately replaced with the function value.
STABLE indicates that within a single table scan the function
will consistently return the same result for the same argument
values, but that its result could change across SQL statements.
This is the appropriate selection for functions whose results
depend on database lookups, parameter variables (such as the
current time zone), etc. Also note that the current_timestamp
family of functions qualify as stable, since their values do
not change within a transaction.
VOLATILE indicates that the function value can change even
within a single table scan, so no optimizations can be made.
Relatively few database functions are volatile in this sense;
some examples are random(), currval(), timeofday(). Note that
any function that has side-effects must be classified volatile,
even if its result is quite predictable, to prevent calls from
being optimized away; an example is setval().
CALLED ON NULL INPUT
RETURNS NULL ON NULL INPUT
STRICT CALLED ON NULL INPUT (the default) indicates that the function
will be called normally when some of its arguments are null. It
is then the function author’s responsibility to check for null
values if necessary and respond appropriately.
RETURNS NULL ON NULL INPUT or STRICT indicates that the func-
tion always returns null whenever any of its arguments are
null. If this parameter is specified, the function is not exe-
cuted when there are null arguments; instead a null result is
assumed automatically.
[EXTERNAL] SECURITY INVOKER
[EXTERNAL] SECURITY DEFINER
SECURITY INVOKER indicates that the function is to be executed
with the privileges of the user that calls it. That is the
default. SECURITY DEFINER specifies that the function is to be
executed with the privileges of the user that created it.
The key word EXTERNAL is present for SQL conformance but is
optional since, unlike in SQL, this feature does not only apply
to external functions.
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 command, or text in a procedural language.
obj_file, link_symbol
This form of the AS clause is used for dynamically loadable 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 function’s
link symbol, that is, the name of the function in the C lan-
guage source code. If the link symbol is omitted, it is assumed
to be the same as the name of the SQL function being defined.
attribute
The historical way to specify optional pieces of information
about the function. The following attributes may appear here:
isStrict
Equivalent to STRICT or RETURNS NULL ON NULL INPUT
isCachable
isCachable is an obsolete equivalent of IMMUTABLE; it’s
still accepted for backwards-compatibility reasons.
Attribute names are not case-sensitive.
NOTES
Refer to [XRef to XFUNC] for further information on writing functions.
The full SQL type syntax is allowed for input arguments and return
value. However, some details of the type specification (e.g., the pre-
cision field for type numeric) 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.
PostgreSQL allows function overloading; that is, the same name can be
used for several different functions so long as they have distinct
argument types. However, the C names of all functions must be differ-
ent, so you must give overloaded C functions different C names (for
example, use the argument types as part of the C names).
When repeated CREATE FUNCTION calls refer to the same object file, the
file is only loaded once. To unload and reload the file (perhaps dur-
ing development), use the LOAD [load(7)] command.
Use DROP FUNCTION to remove user-defined functions.
Any single quotes or backslashes in the function definition must be
escaped by doubling them.
To be able to define a function, the user must have the USAGE privi-
lege on the language.
EXAMPLES
Here is a trivial example to help you get started. For more informa-
tion and examples, see [XRef to XFUNC].
CREATE FUNCTION add(integer, integer) RETURNS integer
AS ’select $1 + $2;’
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
WRITING SECURITY DEFINER FUNCTIONS SAFELY
Because a SECURITY DEFINER function is executed with the privileges of
the user that created it, care is needed to ensure that the function
cannot be misused. For security, search_path should be set to exclude
any schemas writable by untrusted users. This prevents malicious users
from creating objects that mask objects used by the function. Particu-
larly important in this regard is the temporary-table schema, which is
searched first by default, and is normally writable by anyone. A
secure arrangement can be had by forcing the temporary schema to be
searched last. To do this, write pg_temp as the last entry in
search_path. This function illustrates safe usage:
CREATE FUNCTION check_password(TEXT, TEXT)
RETURNS BOOLEAN AS ’
DECLARE passed BOOLEAN;
old_path TEXT;
BEGIN
-- Save old search_path; notice we must qualify current_setting
-- to ensure we invoke the right function
old_path := pg_catalog.current_setting(’’search_path’’);
-- Set a secure search_path: trusted schemas, then ’’pg_temp’’.
-- We set is_local = true so that the old value will be restored
-- in event of an error before we reach the function end.
PERFORM pg_catalog.set_config(’’search_path’’, ’’admin, pg_temp’’, true);
-- Do whatever secure work we came for.
SELECT (pwd = $2) INTO passed
FROM pwds
WHERE username = $1;
-- Restore caller’’s search_path
PERFORM pg_catalog.set_config(’’search_path’’, old_path, true);
RETURN passed;
END;
COMPATIBILITY
A CREATE FUNCTION command is defined in SQL99. The PostgreSQL version
is similar but not fully compatible. The attributes are not portable,
neither are the different available languages.
SEE ALSO
ALTER FUNCTION [alter_function(7)], DROP FUNCTION [drop_function(7)],
GRANT [grant(7)], LOAD [load(7)], REVOKE [revoke(7)], createlang(1)
SQL - Language Statements 2008-01-03 CREATE FUNCTION()
