用户定义异常的抛出，修改120号员工的工资，保证修改后工资不超过8000元

declare
  e_highlimit exception;
  v_sal employees.salary%type;
begin
  update employees
     set salary = salary + 500
   where employeeid = 120
  returning salary into v_sal;
  if v_sal > 8000 then
    raise e_highlimit;
  end if;
exception
  when e_highlimit then
    dbms_output.put_line('the salary is too large');
    rollback;
end;