触发器,修改表里面的字段时将该字段另存到另一字段的触发器

create or replace trigger tb_sm_user_update_trigger
  before update of USER_ORGID on  tb_sm_user 
  for each row
declare
begin
    if :NEW.USER_ORGID!=:OLD.USER_ORGID then 
       :NEW.original_orgid:=:OLD.USER_ORGID;
    end if;
end;

  修改用户表里面的user_orgid 时触发,将user_orgid 值保存到original_orgid 里面.一定要是before才可以,after触发器的话:NEW值就无法修改,报ORG-04084错误.