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以下是SQL SERVER 2000中编写的代码：

SELECT m.shoesid, m.shoesname, m.shoestype, m.shoessize, m.shoescolor, m.shoesprice, m.shoesstate, n.shoesNum
FROM Shoes AS m INNER JOIN
(SELECT a.shoesid, ISNULL(a.x, 0) - ISNULL(b.x, 0) AS shoesNum FROM
(SELECT shoesid, SUM(shoesnum) AS x FROM Stock AS ss GROUP BY shoesid) AS a
LEFT JOIN
(SELECT shoesid, SUM(salesnum) AS x FROM Sales AS cc GROUP BY shoesid) AS b
ON a.shoesid = b.shoesid) AS n ON m.shoesid = n.shoesid

其中：
表Stock ，Shoes ，Sales 为实体对象。
由于系统的数据库可能未知，而上面的SQL语句中用到了SQL SERVER 中特有的函数Isnull。所以如果我用原生SQL来做的话，换了个数据库系统肯定是不行的。
所以请帮忙用HQL实现以上语句，或者用Criteria实现也可以。不胜感激！