如此SQL句能否？
表A
CNo SeqNo sNum dNum
A 1 20
A 2 50
A 3 30

表B
CNo Num
A 80

需得到的果：
CNo SeqNo sNum dNum
A 1 20 20
A 2 50 50
A 3 30 10

也就是依次更新A表中的dNum的值，B表中的Num大於等B表的，A表中的dNum=sNum,小於A中的dNum等於B表中的Num(余下的)


[解决办法]
然可以
[解决办法]
create table 表A(CNo varchar(100), SeqNo int, sNum int, dNum int)
insert into 表A select 'A ', 1, 20,null
insert into 表A select 'A ', 2, 50,null
insert into 表A select 'A ', 3, 30,null

create table 表B (CNo varchar(100), Num int)
insert into 表B select 'A ', 80


select *
from 表A


update 表A set dNum =
case
when sNum <B.Num-isnull((select sum(sNum) from 表A where CNo=a.CNo and SeqNo <a.SeqNo),0) then sNum
else isnull((B.Num-(select sum(sNum) from 表A where CNo=a.CNo and SeqNo <a.SeqNo)),0)
end
from 表A as a
inner join 表B as b on a.CNo=B.CNo

select *
from 表A

drop table 表A,表B
[解决办法]
declare @i int
update A,B set A.dNum=case @i=((@i=B.Num)-A.sNum) when > 0 then A.sNum else @i where A.CNo=B.CNo

试试.
[解决办法]
declare @A table(CNo char(1), SeqNo int, sNum int, dNum int)
insert @A
select 'A ', 1,20,null union all
select 'A ', 2,50,null union all
select 'A ', 3,30,null

declare @B table(CNo char(1), Num int)
insert @B
select 'A ',80

--这是SELECT
select a.CNo,a.SeqNo,a.sNum,
dNum=
case
when b.Num> (select sum(sNum) from @A where SeqNo <=a.SeqNo)
then (select sum(sNum) from @A where SeqNo <=a.SeqNo)
else
b.Num - (select sum(sNum) from @A where SeqNo <a.SeqNo)
end
from @A a, @B b where a.Cno = b.Cno
/*
A12020
A25070
A33010
*/

--这是UPDATE
update a set a.dNum =
case
when b.Num> (select sum(sNum) from @A where SeqNo <=a.SeqNo)
then (select sum(sNum) from @A where SeqNo <=a.SeqNo)
else
b.Num - (select sum(sNum) from @A where SeqNo <a.SeqNo)
end
from @A a, @B b where a.Cno = b.Cno
select * from @A
/*
A12020
A25070
A33010
*/