用SQL找出每种类型中时间最新的前N个数据组成的集合

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