各位大侠快来求命!!!!!
t1   采购表

po_number     item_num       po_qty

po07-01235     001                   500
po07-01235     002                   300
po07-01475     003                   1000

t2收货表
po_number     item_num       in_qty

po07-01235     001                   500
po07-01235     002                   300

t3   退货表

po_number     item_num       out_qty
po07-01235     001                 100


我要结果是:
po_number       item_num       po_qty     in_qty         balance(还有多少未到)
po07-01235       001                   500         400             100  
po07-01235       002                   300         300               0      
po07-01475       003                   1000       0                 1000

只要SQL   语句,谢谢!




------解决方案--------------------
select t1.po_number,t1.item_num,t1.po_qty,t1.in_qty-t2.out_qty,t3.out_qty from
t1 left join t2 on t1.item_num=t2.item_num
join t3 on t2.item_num=t3.item_num

------解决方案--------------------
select distinct t1.po_number,t1.item_num ,t1.po_qty,isnull(t2.in_qty,0) as in_qty,
Convert(int,t1.po_qty)-Convert(int,isnull(t2.in_qty,0) as in_qty) as balance
from ti left join t2 on t1.po_number=t2.po_number left outer join t3 on t1.po_number=t3.po_number

------解决方案--------------------
drop table t1,t2,t3
go
create table t1(po_number varchar(20),item_num varchar(20),po_qty int)
insert into t1
select 'po07-01235 ', '001 ',500
union all select 'po07-01235 ', '002 ',300
union all select 'po07-01475 ', '003 ',1000

create table t2(po_number varchar(20),item_num varchar(20),in_qty int)
insert into t2
select 'po07-01235 ', '001 ',500
union all select 'po07-01235 ', '002 ',300

create table t3(po_number varchar(20),item_num varchar(20),out_qty int)
insert into t3
select 'po07-01235 ', '001 ',100

select t1.po_number,
t1.item_num,
t1.po_qty,
isnull(t2.in_qty,0)-isnull(t3.out_qty,0) as in_qty,
isnull(t1.po_qty,0)-isnull(t2.in_qty,0)+isnull(t3.out_qty,0) as balance
from t1
left join (select po_number,item_num,sum(in_qty) in_qty from t2 group by po_number,item_num)t2 on t1.po_number=t2.po_number and t1.item_num=t2.item_num
left join (select po_number,item_num,sum(out_qty) out_qty from t3 group by po_number,item_num)t3 on t1.po_number=t3.po_number and t1.item_num=t3.item_num
/*
po_number item_num po_qty in_qty balance
-------------------- -------------------- -----------