update 表a a set a.b=(select b.d from 表b b where a.b=b.c) where exists( select 1 from 表b c where a.b=c.c)
update a set b = (select d from b where a.b = b.c)
merge into tb1 t using tb2 s on (t.b=s.c) when matched then update t.b=s.d update tb1 t set t.b=(select d from tb2 s where t.b=s.c) where exists(select 1 from tb2 k where t.b=k.c)
where exists( select 1 from 表b c where a.b=c.c)
when matched then update t.b=s.d
update tb1 t set t.b=(select d from tb2 s where t.b=s.c)
where exists(select 1 from tb2 k where t.b=k.c)