另一个SQL算法问题

[綏子]

三个表
表A
hbbm(编码), sl(数量)
1 2
2 3

表B
hbbm sl1
1 5
2 10
3 4

表c
hbbm sl2
2 3
3 4
5 6

上面三个表的结构完全相同，

要求显示如下结果
hbbm, sl, sl1, sl2
1 2 5 0
2 3 10 3
3 0 4 4
5 0 0 6


不知大侠是否能看懂这个意思.(也就是对三个表合并，但是不像普通的合并)
分只有这么多了，先谢了。

[lifeforu]

select a.hbbm,a.sl,b.sl1,c.sl2 from 表A a,表B b ,表C c
where a.hbbm=b.hbbm and b.hbbm=c.hbbm

[nboys]

select hbbm,sum(s1),sum(s11),sum(s12)
from
(select hbbm,s1,0 as s11,0 as s12 from A
union
select hbbm,0,s11,0 from B
union
select hbbm,0,0,s12 from C) tem
group by hbbm

[nboys]

select hbbm,sum(s1) as s1,sum(s11) as s11,sum(s12) as s12
from
(select hbbm,s1,0 as s11,0 as s12 from A
union all
select hbbm,0,s11,0 from B
union all
select hbbm,0,0,s12 from C) tem
group by hbbm

[happydreamer]

select isnull (isnull(a.hbbm,b.hbbm),c.hbbm) hbbm ,isnull(a.sl,0) s1,isnull(b.sl1,0) sl1 ,isnull(c.sl2,0) sl2
from a full join b on a.hbbm=b.hbbm
full join c on a.hbbm=c.hbbm