MySQL每个分类的前几条记录

MySQL 获取所有分类和每个分类的前几条记录

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

ps:  @N 就是要取多少条