覺得寫的比較好的語句（UPDTAE）

create  table t(id int,num int)

insert into  t select 1,200
insert into  t select 2,10
insert into  t select 3,60
insert into  t select 4,80
insert into  t select 5,600




delete from t
declare @sum int
set @sum=300

update a
set
    num=(case when (select sum(num) from t where id<=a.id)< @sum
                then 0
              when
                   (select sum(num) from t where id< a.id)< @sum
                   and
                   (select sum(num) from t where id<=a.id)>=@sum
                then
                   (select sum(num) from t where id<=a.id)-@sum
              else a.num end)
from
    t a

select * from  t


/*
id          num        
----------- -----------
1           0
2           0
3           0
4           50
5           600
*/

雖然很普通，但讓人啓發很大