表a字段a1,如何与表b字段b1 用触发器同步

a1 字段做修改, 同步到b1
b1 字段做修改, 同步到a1

跑一个job定时同步

a1表改变b1表也改变的触发器（atob）：连接的列为ab,变化的列为bh

create or replace trigger atob
after delete or insert or update on a1 for each row
begin
if inserting then

update b1 set bh=bh+1 where b1.ab=:new.ab;
elsif deleting then
update b1 set bh=bh-1 where b1.ab=:old.ab;
elsif updating then
update b1 set bh=bh+1 where b1.ab=:new.ab;
update b1 set bh=bh-1 where b1.ab=:old.ab;
end if;
end;
/
再写一个b1影响a1表的触发器