NAME¶

CREATE_FUNCTION - define a new function

SYNOPSIS¶

CREATE [ OR REPLACE ] FUNCTION


    name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } default_expr ] [, ...] ] )


    [ RETURNS rettype


      | RETURNS TABLE ( column_name column_type [, ...] ) ]


  { LANGUAGE lang_name


    | TRANSFORM { FOR TYPE type_name } [, ... ]


    | WINDOW


    | { IMMUTABLE | STABLE | VOLATILE }


    | [ NOT ] LEAKPROOF


    | { CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT }


    | { [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER }


    | PARALLEL { UNSAFE | RESTRICTED | SAFE }


    | COST execution_cost


    | ROWS result_rows


    | SUPPORT support_function


    | SET configuration_parameter { TO value | = value | FROM CURRENT }


    | AS 'definition'


    | AS 'obj_file', 'link_symbol'


  } ...

DESCRIPTION¶

CREATE FUNCTION defines a new function. CREATE OR REPLACE FUNCTION will either create a new function, or replace an existing definition. To be able to define a function, the user must have the USAGE privilege on the language.

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 or procedure with the same input argument types in the same schema. However, functions and procedures 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 types of any OUT parameters except by dropping the function.)

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 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.

To be able to create a function, you must have USAGE privilege on the argument types and the return type.

Refer to Section 37.3 for further information on writing functions.

PARAMETERS¶

name

argmode

argname

argtype

default_expr

rettype

column_name

column_type

lang_name

TRANSFORM { FOR TYPE type_name } [, ... ] }

WINDOW

IMMUTABLE
STABLE
VOLATILE

LEAKPROOF

CALLED ON NULL INPUT
RETURNS NULL ON NULL INPUT
STRICT

[EXTERNAL] SECURITY INVOKER
[EXTERNAL] SECURITY DEFINER

PARALLEL

COST execution_cost

ROWS result_rows

SUPPORT support_function

configuration_parameter
value

definition

obj_file, link_symbol

OVERLOADING¶

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. Whether or not you use it, this capability entails security precautions when calling functions in databases where some users mistrust other users; see Section 10.3.

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.

NOTES¶

The full SQL type syntax is allowed for declaring a function's arguments and return value. However, parenthesized type modifiers (e.g., the precision field for type numeric) are discarded by CREATE FUNCTION. Thus for example CREATE FUNCTION foo (varchar(10)) ... is exactly the same as CREATE FUNCTION foo (varchar) ....

When replacing an existing function with CREATE OR REPLACE FUNCTION, there are restrictions on changing parameter names. You cannot change the name already assigned to any input parameter (although you can add names to parameters that had none before). If there is more than one output parameter, you cannot change the names of the output parameters, because that would change the column names of the anonymous composite type that describes the function's result. These restrictions are made to ensure that existing calls of the function do not stop working when it is replaced.

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¶

Add two integers using a SQL function:

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 owns 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 (e.g., tables, functions, and operators) that mask objects intended to be 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 obtained 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;

This function's intention is to access a table admin.pwds. But without the SET clause, or with a SET clause mentioning only admin, the function could be subverted by creating a temporary table named pwds.

Before PostgreSQL version 8.3, the SET clause was not available, and so older functions may contain rather complicated logic to save, set, and restore search_path. The SET clause 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 Section 5.7 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 the SQL standard. 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.

For parameter defaults, the SQL standard specifies only the syntax with the DEFAULT key word. The syntax with = is used in T-SQL and Firebird.

SEE ALSO¶

ALTER FUNCTION (ALTER_FUNCTION(7)), DROP FUNCTION (DROP_FUNCTION(7)), GRANT(7), LOAD(7), REVOKE(7)