Function

ALTER FUNCTION modifies the attributes of a customized function.

Precautions

Only the owner of a function or a system administrator can run this statement. The user who wants to change the owner of a function must be a direct or indirect member of the new owner role. If a function involves operations on temporary tables, the ALTER FUNCTION cannot be used.

Syntax

Modify the additional parameter of the customized function:

ALTER FUNCTION function_name ( [ { [ argmode ] [ argname ] argtype} [, ...] ] )
    action [ ... ] [ RESTRICT ];

The syntax of the action clause is as follows:

{CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT}
 | {IMMUTABLE | STABLE | VOLATILE}
 | {SHIPPABLE | NOT SHIPPABLE}
 | {NOT FENCED | FENCED}
 | [ NOT ] LEAKPROOF
 | { [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER }
 | AUTHID { DEFINER | CURRENT_USER }
 | COST execution_cost
 | ROWS result_rows
 | SET configuration_parameter { { TO | = } { value | DEFAULT }| FROM CURRENT}
 | RESET {configuration_parameter | ALL}

Modify the name of the customized function:

ALTER FUNCTION funname ( [ { [ argmode ] [ argname ] argtype} [, ...] ] )
    RENAME TO new_name;

Modify the owner of the customized function:

ALTER FUNCTION funname ( [ { [ argmode ] [ argname ] argtype} [, ...] ] )
    OWNER TO new_owner;

Modify the schema of the customized function:

ALTER FUNCTION funname ( [ { [ argmode ] [ argname ] argtype} [, ...] ] )
    SET SCHEMA new_schema;

Parameter Description

function_name
Specifies the function name to be modified.

Value range: An existing function name.
argmode
Specifies whether a parameter is an input or output parameter.

Value range: IN, OUT, IN OUT
argname
Indicates the parameter name.

Value range: A string. It must comply with the naming convention.
argtype
Specifies the parameter type.

Value range: A valid type. For details, see Data Types.
CALLED ON NULL INPUT
Declares that some parameters of the function can be invoked in normal mode if the parameter values are NULL. By default, the usage is the same as specifying the parameters.
RETURNS NULL ON NULL INPUT
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.

The usage of RETURNS NULL ON NULL INPUT is the same as that of STRICT.
IMMUTABLE
Indicates that the function always returns the same result if the parameter values are the same.
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 parameter values, but that its result varies by SQL statements.
VOLATILE
Indicates that the function value can change in one table scanning and no optimization is performed.
SHIPPABLE
NOT SHIPPABLE

Indicates whether the function can be pushed down to DNs for execution.
- Functions of the IMMUTABLE type can always be pushed down to the DNs.
- Functions of the STABLE or VOLATILE type can be pushed down to DNs only if their attribute is SHIPPABLE.
LEAKPROOF
Indicates that the function has no side effect and specifies that the parameter includes only the returned value. LEAKPROOF can be set only by a system administrator.
(Optional) EXTERNAL
The objective is to be compatible with SQL. This feature applies to all functions, including external functions.
SECURITY INVOKER
AUTHID CURREN_USER

Declares that the function will be executed according to the permission of the user that invokes it. By default, the usage is the same as specifying the parameters.

SECURITY INVOKER and AUTHID CURREN_USER have the same functions.
SECURITY DEFINER
AUTHID DEFINER

Specifies that the function is to be executed with the permissions of the user that created it.

The usage of AUTHID DEFINER is the same as that of SECURITY DEFINER.
COST execution_cost
A positive number giving the estimated execution cost for the function.

The unit of execution_cost is cpu_operator_cost.

Value range: A positive number.
ROWS result_rows
Estimates the number of rows returned by the function. This is only allowed when the function is declared to return a set.

Value range: A positive number. The default is 1000 rows.
configuration_parameter
- value
  Sets a specified database session parameter to a specified value. If the value is DEFAULT or RESET, the default setting is used in the new session. OFF closes the setting.
  
  Value range: a string
  - DEFAULT
  - OFF
  - RESET
  Specifies the default value.
- from current
  Uses the value of configuration_parameter of the current session.
new_name
Specifies the new name of a function. To change a function's schema, you must also have the CREATE permission on the new schema.

Value range: A string. It must comply with the naming convention.
new_owner
Specifies the new owner of a function. To alter the owner, the new owner must also be a direct or indirect member of the new owning role, and that role must have CREATE permission on the function's schema.

Value range: Existing user roles.
new_schema
Specifies the new schema of a function.

Value range: Existing schemas.

Example

Create a function that calculates the sum of two integers and returns the result. If the input is null, null will be returned.

DROP FUNCTION IF EXISTS func_add_sql2; 
CREATE FUNCTION func_add_sql2(num1 integer, num2 integer) RETURN integer
AS
BEGIN 
RETURN num1 + num2;
END;
/

Alter the execution rule of function add to IMMUTABLE (that is, the same result is returned if the parameter remains unchanged):

ALTER FUNCTION func_add_sql2(INTEGER, INTEGER) IMMUTABLE;

Rename the func_add_sql2 function as add_two_number:

ALTER FUNCTION func_add_sql2(INTEGER, INTEGER) RENAME TO add_two_number;

Change the owner of function add_two_number to dbadmin:

ALTER FUNCTION add_two_number(INTEGER, INTEGER) OWNER TO dbadmin;

Helpful Links

CREATE FUNCTION, DROP FUNCTION