update A
set A.nowtype = '到期'
from A
inner join B on A.STUDENTID=B.STUDENTID and B.Isend='到期'

------解决方案--------------------
SQL code
update A set A.Nowtype='到期'
from A join (
  select STUDENTID 
  from B 
  group by STUDENTID 
  having count(*)=sum(case when Isend='到期' then 1 else 0 end)
)  T on A.STUDENTID=T.STUDENTID

------解决方案--------------------
SQL code
update
 a 
set
 a.Nowtype='到期'
from
 a , 
 (select STUDENTID from B  group by STUDENTID having count(1)=sum(case when Isend='到期' then 1 else 0 end)
)b
where
 a.STUDENTID=b.STUDENTID

------解决方案--------------------
update a set Nowtype = '到期' from a where STUDENTID not in
(select distinct STUDENTID from b where B.Isend <> '到期')


------解决方案--------------------
探讨

update a set Nowtype = '到期' from a where STUDENTID not in
(select distinct STUDENTID from b where B.Isend <> '到期')


这里面，not in应该是in吧？


------解决方案--------------------
探讨

下午散分。谢谢