急！！！！！！！～～～～～～～这个触发器怎么写！
create table a
(
a number(2),
id number(2)
)
create table b
(
b number(2),
id number(2)
)
insert into a (a,id)values(1,9)
insert into b (b,id)values(2,9)


create trigger a_update
before update of a on a
referencing old as old_value
new as new_value
for each row
begin
:new_value.id:=5;
end


drop trigger a_update;

update a set a=5

select *
from a

select*
from b

我想把a表中的a字段改为5，同时b表中的b字段也变成5

[解决办法]