NAME
CREATE FUNCTION - define a new function
SYNOPSIS
CREATE [ OR REPLACE ] FUNCTION
name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } defexpr ] [, ...] ] )
[ RETURNS rettype
| RETURNS TABLE ( colname coltype [, ...] ) ]
{ LANGUAGE langname
| WINDOW
| IMMUTABLE | STABLE | VOLATILE
| CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
| [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
| COST execution_cost
| ROWS result_rows
| SET configuration_parameter { TO value | = value | FROM CURRENT }
| 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 input argument types in the same schema. However, functions of
different argument types can share a name (this is called overloading).
To replace the current 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 cannot 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. Also, ALTER FUNCTION can be used to change most
of the auxiliary properties of an existing function.
The user that creates the function becomes the owner of the function.
PARAMETERS
name The name (optionally schema-qualified) of the function to
create.
argmode
The mode of an argument: IN, OUT, INOUT, or VARIADIC. If
omitted, the default is IN. Only OUT arguments can follow a
VARIADIC one. Also, OUT and INOUT arguments cannot be used
together with the RETURNS TABLE notation.
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
documentation. 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 can be base, composite,
or domain types, or can reference the type of a table column.
Depending on the implementation language it might also be
allowed to specify ‘‘pseudotypes’’ such as cstring. Pseudotypes
indicate that the actual argument type is either incompletely
specified, or outside the set of ordinary SQL data types.
The type of a column is referenced by writing
tablename.columnname%TYPE. Using this feature can sometimes
help make a function independent of changes to the definition of
a table.
defexpr
An expression to be used as default value if the parameter is
not specified. The expression has to be coercible to the
argument type of the parameter. Only input (including INOUT)
parameters can have a default value. All input parameters
following a parameter with a default value must have default
values as well.
rettype
The return data type (optionally schema-qualified). The return
type can be a base, composite, or domain type, or can reference
the type of a table column. Depending on the implementation
language it might also be allowed to specify ‘‘pseudotypes’’
such as cstring. If the function is not supposed to return a
value, specify void as the return type.
When there are OUT or INOUT parameters, the RETURNS clause can
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
parameter.
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.columnname%TYPE.
colname
The name of an output column in the RETURNS TABLE syntax. This
is effectively another way of declaring a named OUT parameter,
except that RETURNS TABLE also implies RETURNS SETOF.
coltype
The data type of an output column in the RETURNS TABLE syntax.
langname
The name of the language that the function is implemented in.
Can be SQL, C, internal, or the name of a user-defined
procedural language. For backward compatibility, the name can be
enclosed by single quotes.
WINDOW WINDOW indicates that the function is a window function rather
than a plain function. This is currently only useful for
functions written in C. The WINDOW attribute cannot be changed
when replacing an existing function definition.
IMMUTABLE
STABLE
VOLATILE
These attributes inform the query optimizer about the behavior
of the function. At most one choice can be specified. If none of
these appear, VOLATILE is the default assumption.
IMMUTABLE indicates that the function cannot modify the database
and 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 the function cannot modify the database,
and that within a single table scan it 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 in 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
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 allowed for SQL conformance, but it is
optional since, unlike in SQL, this feature applies to all
functions not only external ones.
execution_cost
A positive number giving the estimated execution cost for the
function, in units of cpu_operator_cost. If the function returns
a set, this is the cost per returned row. If the cost is not
specified, 1 unit is assumed for C-language and internal
functions, and 100 units for functions in all other languages.
Larger values cause the planner to try to avoid evaluating the
function more often than necessary.
result_rows
A positive number giving the estimated number of rows that the
planner should expect the function to return. This is only
allowed when the function is declared to return a set. The
default assumption is 1000 rows.
configuration_parameter
value The SET clause causes the specified configuration parameter to
be set to the specified value when the function is entered, and
then restored to its prior value when the function exits. SET
FROM CURRENT saves the session’s current value of the parameter
as the value to be applied when the function is entered.
See SET [set(7)] and in the documentation for more information
about allowed parameter names and values.
definition
A string constant defining the function; the meaning depends on
the language. It can 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 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 can 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 in the documentation 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
precision field for type numeric) 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
input argument types. However, the C names of all functions must be
different, 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) ...
Functions that have different argument type lists will not be
considered to conflict at creation time, but if defaults are provided
they might conflict in use. For example, consider
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, int default 42) ...
A call foo(10) will fail due to the ambiguity about which function
should be called.
When repeated CREATE FUNCTION calls refer to the same object file, the
file is only loaded once per session. To unload and reload the file
(perhaps during development), start a new session.
Use DROP FUNCTION [drop_function(7)] to remove user-defined functions.
It is often helpful to use dollar quoting (see in 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.
If a SET clause is attached to a function, then the effects of a SET
LOCAL command executed inside the function for the same variable are
restricted to the function: the configuration parameter’s prior value
is still restored at function exit. However, an ordinary SET command
(without LOCAL) overrides the SET clause, much as it would do for a
previous SET LOCAL command: the effects of such a command will persist
after function exit, unless the current transaction is rolled back.
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
function, 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).
If a function is declared STRICT with a VARIADIC argument, the
strictness check tests that the variadic array as a whole is non-null.
The function will still be called if the array has null elements.
EXAMPLES
Here are some trivial examples to help you get started. For more
information and examples, see in 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
composite 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);
Another way to return multiple columns is to use a TABLE function:
CREATE FUNCTION dup(int) RETURNS TABLE(f1 int, f2 text)
AS $$ SELECT $1, CAST($1 AS text) || ’ is text’ $$
LANGUAGE SQL;
SELECT * FROM dup(42);
However, a TABLE function is different from the preceding examples,
because it actually returns a set of records, not just one record.
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.
Particularly 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 $$
DECLARE passed BOOLEAN;
BEGIN
SELECT (pwd = $2) INTO passed
FROM pwds
WHERE username = $1;
RETURN passed;
END;
$$ LANGUAGE plpgsql
SECURITY DEFINER
-- Set a secure search_path: trusted schema(s), then ’pg_temp’.
SET search_path = admin, pg_temp;
Before PostgreSQL version 8.3, the SET option was not available, and so
older functions may contain rather complicated logic to save, set, and
restore search_path. The SET option is far easier to use for this
purpose.
Another point to keep in mind is that by default, execute privilege is
granted to PUBLIC for newly created functions (see GRANT [grant(7)] for
more information). Frequently you will wish to restrict use of a
security definer function to only some users. To do that, you must
revoke the default PUBLIC privileges and then grant execute privilege
selectively. To avoid having a window where the new function is
accessible to all, create it and set the privileges within a single
transaction. For example:
BEGIN;
CREATE FUNCTION check_password(uname TEXT, pass TEXT) ... SECURITY DEFINER;
REVOKE ALL ON FUNCTION check_password(uname TEXT, pass TEXT) FROM PUBLIC;
GRANT EXECUTE ON FUNCTION check_password(uname TEXT, pass TEXT) TO admins;
COMMIT;
COMPATIBILITY
A CREATE FUNCTION command is defined in SQL:1999 and later. The
PostgreSQL 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.
The SQL standard does not specify parameter defaults. The syntax with
the DEFAULT key word is from Oracle, and it is somewhat in the spirit
of the standard: SQL/PSM uses it for variable default values. The
syntax with = is used in T-SQL and Firebird.
SEE ALSO
ALTER FUNCTION [alter_function(7)], DROP FUNCTION [drop_function(7)],
GRANT [grant(7)], LOAD [load(7)], REVOKE [revoke(7)], createlang
[createlang(1)]