create_function(7)

NAME#

CREATE_FUNCTION - define a new function

SYNOPSIS#

CREATE [ OR REPLACE ] FUNCTION
\n
    \nname\n ( [ [ \nargmode\n ] [ \nargname\n ] \nargtype\n [ { DEFAULT | = } \ndefault_expr\n ] [, ...] ] )
\n
    [ RETURNS \nrettype\n
\n
      | RETURNS TABLE ( \ncolumn_name\n \ncolumn_type\n [, ...] ) ]
\n
  { LANGUAGE \nlang_name\n
\n
    | TRANSFORM { FOR TYPE \ntype_name\n } [, ... ]
\n
    | WINDOW
\n
    | { IMMUTABLE | STABLE | VOLATILE }
\n
    | [ NOT ] LEAKPROOF
\n
    | { CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT }
\n
    | { [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER }
\n
    | PARALLEL { UNSAFE | RESTRICTED | SAFE }
\n
    | COST \nexecution_cost\n
\n
    | ROWS \nresult_rows\n
\n
    | SUPPORT \nsupport_function\n
\n
    | SET \nconfiguration_parameter\n { TO \nvalue\n | = \nvalue\n | FROM CURRENT }
\n
    | AS '\ndefinition\n'
\n
    | AS '\nobj_file\n', '\nlink_symbol\n'
\n
    | \nsql_body\n
\n
  } ...

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 36.3 for further information on writing functions.

PARAMETERS#

name

argmode

argname

argtype

Depending on the implementation language it might 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.

The type of a column is referenced by writing table_name.column_name%TYPE. Using this feature can sometimes help make a function independent of changes to the definition of a table.

default_expr

rettype

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 table_name.column_name%TYPE.

column_name

column_type

lang_name

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

WINDOW

IMMUTABLE STABLE VOLATILE

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. (It is inappropriate for AFTER triggers that wish to query rows modified by the current command.) 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 Section 36.7.

LEAKPROOF

CALLED ON NULL INPUT RETURNS NULL ON NULL INPUT STRICT

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

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.

PARALLEL

Functions should be labeled parallel unsafe if they modify any database state, change the transaction state (other than by using a subtransaction for error recovery), access sequences (e.g., by calling currval) or make persistent changes to settings. They should be labeled parallel restricted if they access temporary tables, client connection state, cursors, prepared statements, or miscellaneous backend-local state which the system cannot synchronize in parallel mode (e.g., setseed cannot be executed other than by the group leader because a change made by another process would not be reflected in the leader). In general, if a function is labeled as being safe when it is restricted or unsafe, or if it is labeled as being restricted when it is in fact unsafe, it may throw errors or produce wrong answers when used in a parallel query. C-language functions could in theory exhibit totally undefined behavior if mislabeled, since there is no way for the system to protect itself against arbitrary C code, but in most likely cases the result will be no worse than for any other function. If in doubt, functions should be labeled as UNSAFE, which is the default.

COST execution_cost

ROWS result_rows

SUPPORT support_function

configuration_parameter value

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.

See SET(7) and Chapter 19 for more information about allowed parameter names and values.

definition

It is often helpful to use dollar quoting (see Section 4.1.2.4) 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.

obj_file, link_symbol

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.

sql_body

RETURN \nexpression

or a block

BEGIN ATOMIC
\n
  \nstatement\n;
\n
  \nstatement\n;
\n
  ...
\n
  \nstatement\n;
END

This is similar to writing the text of the function body as a string constant (see definition above), but there are some differences: This form only works for LANGUAGE SQL, the string constant form works for all languages. This form is parsed at function definition time, the string constant form is parsed at execution time; therefore this form cannot support polymorphic argument types and other constructs that are not resolvable at function definition time. This form tracks dependencies between the function and objects used in the function body, so DROP ... CASCADE will work correctly, whereas the form using string literals may leave dangling functions. Finally, this form is more compatible with the SQL standard and other SQL implementations.

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 an SQL function:

CREATE FUNCTION add(integer, integer) RETURNS integer
\n
    AS 'select $1 + $2;'
\n
    LANGUAGE SQL
\n
    IMMUTABLE
\n
    RETURNS NULL ON NULL INPUT;

The same function written in a more SQL-conforming style, using argument names and an unquoted body:

CREATE FUNCTION add(a integer, b integer) RETURNS integer
\n
    LANGUAGE SQL
\n
    IMMUTABLE
\n
    RETURNS NULL ON NULL INPUT
\n
    RETURN a + b;

Increment an integer, making use of an argument name, in PL/pgSQL:

CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
\n
        BEGIN
\n
                RETURN i + 1;
\n
        END;
$$ LANGUAGE plpgsql;

Return a record containing multiple output parameters:

CREATE FUNCTION dup(in int, out f1 int, out f2 text)
\n
    AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
\n
    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
\n
    AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
\n
    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)
\n
    AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
\n
    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 $$
DECLARE passed BOOLEAN;
BEGIN
\n
        SELECT  (pwd = $2) INTO passed
\n
        FROM    pwds
\n
        WHERE   username = $1;
\n
        RETURN passed;
END;
$$  LANGUAGE plpgsql
\n
    SECURITY DEFINER
\n
    -- Set a secure search_path: trusted schema(s), then 'pg_temp'.
\n
    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.

If the security definer function intends to create roles, and if it is running as a non-superuser, createrole_self_grant should also be set to a known value using the SET clause.

Another point to keep in mind is that by default, execute privilege is granted to PUBLIC for newly created functions (see Section 5.8 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 implementation can be used in a compatible way but has many extensions. Conversely, the SQL standard specifies a number of optional features that are not implemented in PostgreSQL.

The following are important compatibility issues:

Simple LANGUAGE SQL functions can be written in a way that is both standard-conforming and portable to other implementations. More complex functions using advanced features, optimization attributes, or other languages will necessarily be specific to PostgreSQL in a significant way.

SEE ALSO#

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