stock表，结构与记录如下：
日期(rdate) 数量(qty) 进出(dc)
4/1 40 1
4/1 50 1
4/5 20 -1
4/15 10 1
4/20 20 -1

希望生成这样的表
日期 余额
4/1 90
4/2 90
4/3 90
4/4 90
4/5 70
4/6 70
...
4/14 70
4/15 80
4/16 80
...
4/20 60
...
create table stock
(rdate char(10),
qty int,
dc int)
insert into stock values ('2012-04-01',40,1)
insert into stock values ('2012-04-01',50,1)
insert into stock values ('2012-04-05',20,-1)
insert into stock values ('2012-04-15',10,1)
insert into stock values ('2012-04-20',20,-1)
select date as rdate,qty=(select sum(qty*dc) from stock where rdate<=a.date) from
(select convert(char(10),dateadd(day,number,'2012-04-01'),23) as date from master.dbo.spt_values where type='P' and number<=30)
a 

----结果
rdate   qty
2012-04-01    90
2012-04-02    90
2012-04-03    90
2012-04-04    90
2012-04-05    70
2012-04-06    70
2012-04-07    70
2012-04-08    70
2012-04-09    70
2012-04-10    70
2012-04-11    70
2012-04-12    70
2012-04-13    70
2012-04-14    70
2012-04-15    80
2012-04-16    80
2012-04-17    80
2012-04-18    80
2012-04-19    80
2012-04-20    60
2012-04-21    60
2012-04-22    60
2012-04-23    60
2012-04-24    60
2012-04-25    60
2012-04-26    60
2012-04-27    60
2012-04-28    60
2012-04-29    60
2012-04-30    60
2012-05-01    60