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CREATE
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.
The user that creates the function becomes the owner of the function.
"PARAMETERS"
name The name of a function to create. If a schema name is included, then
the function is created in the specified schema. Otherwise it is
created in the current schema (the one at the front of the search
path; see 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).
argtype
The data type(s) of the function's arguments, if any. The input types
may be base, complex, or domain types, or the same as the type of an
existing column. The type of a column is referenced by writing
tablename.columnname%TYPE; using this can sometimes help make a
function independent from changes to the definition of a table.
Depending on the implementation language it may also be allowed to
specify ``pseudo-types'' such as cstring. Pseudo-types indicate that
the actual argument type is either incompletely specified, or outside
the set of ordinary SQL data types.
rettype
The return data type. The return type may be specified as a base,
complex, or domain type, or the same as the type of an existing
column. Depending on the implementation language it may also be
allowed to specify ``pseudo-types'' 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 procedural language.
(See also createlang [createlang(1)].) 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 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
parameter 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 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 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 compatibility 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 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.
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 chapter in the PostgreSQL Programmer's Guide on the topic of
extending PostgreSQL via functions for further information on writing
external functions.
The full SQL type syntax is allowed for input arguments and return value.
However, some details of the type specification (e.g., the precision field
for numeric types) are the responsibility of the underlying function
implementation and are silently swallowed (i.e., not recognized 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. 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.
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(5)] command.
Use DROP FUNCTION to remove user-defined functions.
To update the definition of an existing function, use CREATE OR REPLACE
FUNCTION. Note that 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 re-create the function.
If you drop and then re-create a function, the new function is not the same
entity as the old; you will break existing rules, views, triggers, 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.
To be able to define a function, the user must have the USAGE privilege on
the language.
By default, only the owner (creator) of the function has the right to
execute it. Other users must be granted the EXECUTE privilege on the
function to be able to use it.
EXAMPLES
To create a simple SQL function:
CREATE FUNCTION one() RETURNS integer
AS 'SELECT 1 AS RESULT;'
LANGUAGE SQL;
SELECT one() AS answer;
answer
--------
1
The next example creates a C function by calling a routine from a user-
created shared library named funcs.so (the extension may vary across
platforms). The shared library file is sought in the server's dynamic
library search path. 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 constraint.
CREATE FUNCTION ean_checkdigit(char, char) RETURNS boolean
AS 'funcs' 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))
);
The next example creates a function that does type conversion from the
user-defined type complex to the built-in type point. The function is
implemented by a dynamically loaded object that was compiled from C source
(we illustrate the now-deprecated alternative of specifying the absolute
file name to the shared object file). For PostgreSQL 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 STRICT;
The C declaration of the function could be:
Point * complex_to_point (Complex *z)
{
Point *p;
p = (Point *) palloc(sizeof(Point));
p->x = z->x;
p->y = z->y;
return p;
}
Note that the function is marked ``strict''; this allows us to skip
checking for NULL input in the function body.
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
DROP FUNCTION [drop_function(5)], GRANT [grant(5)], LOAD [load(5)], REVOKE
[revoke(5)], createlang(1), PostgreSQL Programmer's Guide
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Index for
Section FUNCTION |
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Alphabetical
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Top of
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