IF OBJECT_ID('tbl_a') IS NOT NULL DROP table tbl_a
GO 
create table tbl_a(A varchar(10) ,B int ,C int,D int )

insert into tbl_a values('期初',0,0,102)
insert into tbl_a values('1',1,2,0)
insert into tbl_a values('1',1,5,0)
insert into tbl_a values('1',2,5,0)
insert into tbl_a values('1',3,5,0)
insert into tbl_a values('1',4,5,0)
insert into tbl_a values('1',4,7,0)
insert into tbl_a values('1',4,8,0)
insert into tbl_a values('1',5,8,0)

select * from tbl_a

-------------------------------第二一下代码 想实现(表tbl_a) D=D+B-C   
----------执行下代码会提示 ：：
--消息 16931，级别 16，状态 1，第 15 行
--当前提取缓冲区内没有行。
declare @num int,@ii int
select @num=COUNT(*) from tbl_a
set @ii=1

declare my_cursor cursor scroll dynamic for select B,C,D from tbl_a   
open my_cursor   
declare @a int ,@b int ,@c int ,@aa int ,@bb int,@cc int,@dd int

fetch next from my_cursor into @a ,@b ,@c
while(@@fetch_status=0)   
begin   

    if @ii=1   
        set @cc=@c
    

    fetch next from my_cursor into @a ,@b ,@c  
    if @@fetch_status=0
        update tbl_a set D=@cc+@a-@b  where current of my_cursor       
    set @ii=@ii+1
    
    set @cc=@cc+@a-@b
end   

close my_cursor   
deallocate my_cursor   

select * from tbl_a