请问这个SQL怎么写(在线等待)

[WeiXuBin]

请问这个SQL怎么写
xhdml

djh(单据号)khdm(客户代码) kdrq(月份)
1 01 1
2 02 1
3 01 2
. . .
. . .
. . .
100 20 4

xhdnr

djh(单据号)spdm(商品代码) sl(数量)
1 A01 20
1 A02 10
2 B01 30
3 A01 10
. . .
. . .
. . .
100 G25 96

请问怎么得出：
1-4月份各个客户购买各个商品的的数量
请用一行来显示（如果是NULL，请设为0）

请各位帮忙!

[WeiXuBin]

还有一个附加说明:
xhdml：销货单目录
xhdnr: 销货单内容

只能用一句SQL来写

[firetoucher]

select kdrq, khdm, spdm, sum(sl)
from xhdml a, xhdnr b
where a.djh = b.djh
and a.kdrq >= 1 and a.kdrq <= 4
group by kdrq, khdm, spdm

[firetoucher]

？？一行显示？什么意思？

[WeiXuBin]

to: firetoucher(蹈火者)
一行显示是：四个月份分别显示在一行上

kdrq, khdm, spdm, sl1, sl2, sl3, sl4 --fields
^^(1月份数) ^^(2月份数)....

[WeiXuBin]

更正：
kdrq, khdm, spdm, sl1, sl2, sl3, sl4 --fields
^^(1月份数) ^^(2月份数)....
改成

khdm, spdm, sl1, sl2, sl3, sl4 --fields
^^(1月份数) ^^(2月份数)....

[米多]

select khdm,spdm,sum(sl1) as sl1,sum(sl2) as sl1,sum(sl3) as sl3,sum(sl4) as sl4
from
( select khdm,spdm,(case kdrq when 1 then sum(sl) end) as sl1, (case kdrq when 2 then sum(sl) end) as sl2,(case kdrq when 3 then sum(sl) end) as sl3,(case kdrq when 4 then sum(sl) end) as sl4 from xhdml l inner join xhdnr r on l.djh=r.djh group by khdm,spdm,kdrq ) as dd
group by khdm,spdm
order by khdm,spdm