SQL中的查询问题(30分)

Select a.prno,a.OrigQty,
(select sum(qtyP) from Invlist c where c.prno=a.prno ) as InQty,
(select sum(qtyP) from Invlist c where c.prno=a.prno ) as outQty,
(select sum(qtyP) from Invlist c where c.prno=a.prno ) as rtnQty
from invcheck a
上述查询结果只显示prno,origqty字段值，inqty,outqty,rtnqty显示都为空值。
但表invcheck和invlist中都有prno=1001的纪录，如果直接使用该查询语句
select sum(qtyP) from Invlist c where c.prno=1001怎显示出正确的sum(qtyp)值。
不知什么地方出了问题。我用的数据库是Paradox.

SELECT a.prno, a.OrigQty, B.INQTY AS InQty, C.OUTQTY AS outQty,
C.RTNQTY AS rtnQty
FROM invcheck a CROSS JOIN
(SELECT SUM(qtyP) AS INQTY
FROM Invlist c
WHERE c.prno = a.prno) B CROSS JOIN
(SELECT SUM(qtyP) AS OUTQTY
FROM Invlist c
WHERE c.prno = a.prno) C CROSS JOIN
(SELECT SUM(qtyP) AS RTNQTY
FROM Invlist c
WHERE c.prno = a.prno) D
这样试试

用另一方法吧
可以在计算字段中写

To:天真
该语句对paradox好像不支持!?

Select a.prno,a.OrigQty,sum(qtyP) as inqty
from invcheck a
group by a.prno,a.OrigQty

select sum(qtyP) from Invlist c ,invcheck a where c.prno=a.prno
是可行的。

你的SQL本身也有问题，至少表达的意思不明确。