只能在工作时间内更新某表

例如规定只能在工作时间内更新student表，可以定义如下触发器，其中sysdate为系统当前时间

create or replace trigger secure_student
   before insert or update or delete
   on student
begin
   if    (to_char (sysdate, 'dy') in ('sat', 'sun'))
      or (to_number (sysdate, 'hh24') not between 8 and 17)
   then
      raise_application_error
                    (-20506,
                     'you may only change data during normal business hours.'
                    );
   end if;
end;