create_function manpage
CREATE FUNCTION() SQL Commands CREATE FUNCTION()
NAME
CREATE FUNCTION - define a new function
SYNOPSIS
CREATE [ OR REPLACE ] FUNCTION
name ( [ [ argmode ] [ argname ] 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 spec-
ified 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 different
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 would actually 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. (When using OUT parameters, that means
you can't change the names or types of any OUT parameters except by
dropping the function.)
If you drop and then recreate a function, the new function is not the
same entity as the old; you will have to drop existing rules, views,
triggers, etc. that refer 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 (optionally schema-qualified) of the function to cre-
ate.
argmode
The mode of an argument: either IN, OUT, or INOUT. If omitted,
the default is IN.
argname
The name of an argument. Some languages (currently only
PL/pgSQL) let you use the name in the function body. For other
languages the name of an input argument is just extra documenta-
tion. But the name of an output argument is significant, since
it defines the column name in the result row type. (If you omit
the name for an output argument, the system will choose a
default column name.)
argtype
The data type(s) of the function's arguments (optionally schema-
qualified), if any. The argument types may be base, composite,
or domain types, or may reference the type of a table column.
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 speci-
fied, or outside the set of ordinary SQL data types.
The type of a column is referenced by writing tablename.column-
name%TYPE. Using this feature can sometimes help make a func-
tion independent of changes to the definition of a table.
rettype
The return data type (optionally schema-qualified). The return
type may be a base, composite, or domain type, or may reference
the type of a table column. Depending on the implementation
language it may also be allowed to specify ``pseudotypes'' such
as cstring.
When there are OUT or INOUT parameters, the RETURNS clause may
be omitted. If present, it must agree with the result type
implied by the output parameters: RECORD if there are multiple
output parameters, or the same type as the single output parame-
ter.
The SETOF modifier indicates that the function will return a set
of items, rather than a single item.
The type of a column is referenced by writing tablename.column-
name%TYPE.
langname
The name of the language that the function is implemented in.
May be SQL, C, internal, or the name of a user-defined procedur-
al language. For backward 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 may 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(). But 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().
For additional details see the documentation.
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 function
always returns null whenever any of its arguments are null. If
this parameter is specified, the function is not executed when
there are null arguments; instead a null result is assumed auto-
matically.
[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 allowed for SQL conformance, but it is
optional since, unlike in SQL, this feature applies to all func-
tions not only external ones.
definition
A string constant defining the function; the meaning depends on
the language. It may be an internal function name, the path to
an object file, an SQL command, or text in a procedural lan-
guage.
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 dynami-
cally loadable object, and link_symbol is the function's link
symbol, that is, the name of the function in the C language
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 the documentation for further information on writing func-
tions.
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 underlying
function implementation and are silently swallowed (i.e., not recog-
nized 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).
Two functions are considered the same if they have the same names and
input argument types, ignoring any OUT parameters. Thus for example
these declarations conflict:
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, out text) ...
When repeated CREATE FUNCTION calls refer to the same object file, the
file is only loaded once. To unload and reload the file (perhaps during
development), use the LOAD [load(7)] command.
Use DROP FUNCTION [drop_function(7)] to remove user-defined functions.
It is often helpful to use dollar quoting (see the documentation) to
write the function definition string, rather than the normal single
quote syntax. Without dollar quoting, 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 privilege
on the language.
When CREATE OR REPLACE FUNCTION is used to replace an existing func-
tion, the ownership and permissions of the function do not change. All
other function properties are assigned the values specified or implied
in the command. You must own the function to replace it (this includes
being a member of the owning role).
EXAMPLES
Here are some trivial examples to help you get started. For more infor-
mation and examples, see the documentation.
CREATE FUNCTION add(integer, integer) RETURNS integer
AS 'select $1 + $2;'
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
Increment an integer, making use of an argument name, in PL/pgSQL:
CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
BEGIN
RETURN i + 1;
END;
$$ LANGUAGE plpgsql;
Return a record containing multiple output parameters:
CREATE FUNCTION dup(in int, out f1 int, out f2 text)
AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
LANGUAGE SQL;
SELECT * FROM dup(42);
You can do the same thing more verbosely with an explicitly named com-
posite type:
CREATE TYPE dup_result AS (f1 int, f2 text);
CREATE FUNCTION dup(int) RETURNS dup_result
AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
LANGUAGE SQL;
SELECT * FROM dup(42);
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(uname TEXT, pass TEXT)
RETURNS BOOLEAN AS $$
DECLARE passed BOOLEAN;
old_path TEXT;
BEGIN
-- Save old search_path; notice we must qualify current_setting
-- to ensure we invoke the right function
old_path := pg_catalog.current_setting('search_path');
-- Set a secure search_path: trusted schemas, then 'pg_temp'.
-- We set is_local = true so that the old value will be restored
-- in event of an error before we reach the function end.
PERFORM pg_catalog.set_config('search_path', 'admin, pg_temp', true);
-- Do whatever secure work we came for.
SELECT (pwd = $2) INTO passed
FROM pwds
WHERE username = $1;
-- Restore caller's search_path
PERFORM pg_catalog.set_config('search_path', old_path, true);
RETURN passed;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;
COMPATIBILITY
A CREATE FUNCTION command is defined in SQL:1999 and later. The Post-
greSQL version is similar but not fully compatible. The attributes are
not portable, neither are the different available languages.
For compatibility with some other database systems, argmode can be
written either before or after argname. But only the first way is
standard-compliant.
SEE ALSO
ALTER FUNCTION [alter_function(7)], DROP FUNCTION [drop_function(l)],
GRANT [grant(l)], LOAD [load(l)], REVOKE [revoke(l)], createlang [cre-
atelang(1)]
SQL - Language Statements 2010-12-14 CREATE FUNCTION()
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