CREATE FUNCTION function_name (arguments)
RETURNS return_data_type
[ DETERMINISTIC | NOT DETERMINISTIC ]
BEGIN
    -- function statements
   RETURN data;
END
$$

-- DETERMINISTIC - returns same result for same input data.
-- NOT DETERMINISTIC - returns different result for same input data.

-- To see source
SHOW CREATE FUNCTION function_name;

-- To show all functions
SHOW FUNCTION STATUS;

DROP FUNCTION function_name;
Or
DROP FUNCTION IF EXISTS function_name;