帮我看下这触发器是否有错

create or replace trigger SM_lOG_TRI
before update
on SM_OR
for each row
declare
messagetext varchar2(200);
begin
messagetext:='_';
if :new.tr_no <> :old.tr_no THEN

   messagetext:=CONCAT(:new.tr_no);
 end if;

insert into SM_lOG_lOG values(:old.sales_order_id.,:old.create_user,sysdate,messagetext);
end;