不用循环游标，一句update代码实现滚动计算

发现一段经典sql，不用循环游标，一句update代码实现滚动计算结存。为方便理解，结合实例测试之

--1，源数据#t1，jcshl初值为每个sid的当前库存数量，要实现的效果：每个sid的后一结存数量为前一jcshl结存数量-chkshl出库数量
select * from #t1 order by sn

sn plh sid chkshl jcshl
1 s0002 20.0000 980.0000
2 s0003 10.0000 1010.0000
3 s0003 10.0000 1010.0000
4 s0003 10.0000 1010.0000
5 s0002 10.0000 980.0000
6 s0002 1.0000 980.0000
7 s0004 20.0000 720.0000
8 s0005 10.0000 530.0000
9 s0005 10.0000 530.0000
10 s0005 10.0000 530.0000
11 s0004 10.0000 720.0000
12 s0004 1.0000 720.0000

--2，按sid排序#t2，数据顺序决定分组及计算顺序
select * into #t2 from #t1 order by sid,sn

sn plh sid chkshl jcshl
1 s0002 20.0000 980.0000
5 s0002 10.0000 980.0000
6 s0002 1.0000 980.0000
2 s0003 10.0000 1010.0000
3 s0003 10.0000 1010.0000
4 s0003 10.0000 1010.0000
7 s0004 20.0000 720.0000
11 s0004 10.0000 720.0000
12 s0004 1.0000 720.0000
8 s0005 10.0000 530.0000
9 s0005 10.0000 530.0000
10 s0005 10.0000 530.0000

--3，滚动更新jcshl结存数量，同时填入新的plh排列号
declare @plh char(11),@jcshl decimal(18,4),@sid char(11)

update #t2 set 
    @jcshl=jcshl=case when sid=@sid then @jcshl-chkshl else jcshl-chkshl end,
    @plh=plh=str(isnull(@plh,0))+1,
    @sid=sid=sid

select * from #t2

sn plh sid chkshl jcshl
1 1 s0002 20.0000 960.0000
5 2 s0002 10.0000 950.0000
6 3 s0002 1.0000 949.0000
2 4 s0003 10.0000 1000.0000
3 5 s0003 10.0000 990.0000
4 6 s0003 10.0000 980.0000
7 7 s0004 20.0000 700.0000
11 8 s0004 10.0000 690.0000
12 9 s0004 1.0000 689.0000
8 10 s0005 10.0000 520.0000
9 11 s0005 10.0000 510.0000
10 12 s0005 10.0000 500.0000