用SQL找出每种类型中时间最新的前N个数据组成的集合的方法

比如有文章表 Article(Id,Category,InsertDate)
现在要用SQL找出每种类型中时间最新的前N个数据组成的集合
SELECT A1.*  
FROM Article AS A1  
     INNER JOIN (SELECT A.Category,A.InsertDate
                 FROM Article AS A  
                      LEFT JOIN Article AS B  
                        ON A.Category = B.Category  
                           AND A.InsertDate <= B.InsertDate  
                 GROUP BY A.Category,A.InsertDate
                 HAVING COUNT(B.InsertDate) <= @N
    ) AS B1  
    ON A1.Category = B1.Category  
       AND A1.InsertDate = B1.InsertDate
ORDER BY A1.Category,A1.InsertDate DESC

@N 就是你要取多少条