很急，请大家帮帮忙写个查询语句！~非常感谢

Question

select
    a.fh,
    a.item,
    a.y_price,
    f_price=isnull(b.f_price,0),
    t_price=isnull(c.t_price,0),
    [欠款] =a.y_price-isnull(b.f_price,0)-isnull(c.t_price,0)
from
    tb1 a
left join
    tb2 b
on
    a.fh=b.fh and a.item=b.item
left join
    tb3 c
on
    a.fh=c.fh and a.item=c.item and b.bh=c.bh

Answer 1

[欠款] =a.y_price-isnull(b.f_price,0)-isnull(c.t_price,0)
不是这样的公式，请再查一下欠款这项数字，谢谢

Answer 2

declare @tb1 table(fh varchar(20),item varchar(20),y_price int)
insert into @tb1 select 'a1','电费',100
insert into @tb1 select 'a1','房租',800
insert into @tb1 select 'a1','水费',30declare @tb2 table(fh varchar(20),bh varchar(20),item varchar(20),f_price int)
insert into @tb2 select 'a1','b1','房租',500
insert into @tb2 select 'a1','b2','房租',200
insert into @tb2 select 'a1','  ','房租',300
insert into @tb2 select 'a1','  ','水费',30declare @tb3 table(fh varchar(20),bh varchar(20),item varchar(20),t_price int)
insert into @tb3 select 'a1','b1','房租',100
insert into @tb3 select 'a1','b2','房租',100declare @tb4 table(id int identity(1,1),fh varchar(20),bh varchar(20),item varchar(20),f_price int)
insert into @tb4 select * from @tb2
select
    a.fh,
    a.item,
    a.y_price,
    f_price=isnull(b.f_price,0),
    t_price=isnull(c.t_price,0),
    [欠款] =a.y_price-isnull((select 
                                  sum(e.f_price-isnull(f.t_price,0)) 
                              from 
                                  @tb4 e 
                              left join 
                                  @tb3 f 
                              on 
                                  e.fh=f.fh and e.item=f.item and e.bh=f.bh 
                              where 
                                  e.item=b.item and e.fh=b.fh and e.id<=b.id),0)
from
    @tb1 a
left join
    @tb4 b
on
    a.fh=b.fh and a.item=b.item
left join
    @tb3 c
on
    a.fh=c.fh and a.item=c.item and b.bh=c.bh
/*
fh                   item                 y_price     f_price     t_price     欠款          
-------------------- -------------------- ----------- ----------- ----------- ----------- 
a1                   电费                   100         0           0           100
a1                   房租                   800         500         100         400
a1                   房租                   800         200         100         300
a1                   房租                   800         300         0           0
a1                   水费                   30          30          0           0
*/

Answer 3

a1  b1  房租   500
 a1  b2  房租   200
 a1      房租   300
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以上三条记录怎样确定先后顺序？按照在表里的物理顺序？