MySQL獲取全部分類和每一個分類的前N條記錄

好比有文章表 Article(Id,Category,InsertDate)，如今要用SQL找出每種類型中時間最新的前N個數據組成的集合，一段不錯的代碼，留存備用，轉自(loveyuki.com)，感謝。

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 就是你要取多少條

下面是我用到了一個產品分類表中，superId是大分類，prcid是產品分類。能用SQL完成的功能就要儘可能用SQL語句來完成，這既簡潔又高效。

SELECT
    A1.*
FROM
    prcKx AS A1
INNER JOIN (
    SELECT
        A.superId,
        A.prcid
    FROM
        prcKx AS A
    LEFT JOIN prcKx AS B ON A.superId = B.superId
    AND A.prcid <= B.prcid
    GROUP BY
        A.superId,
        A.prcid
    HAVING
        COUNT(B.prcid) <= 7
) AS B1 ON A1.superId = B1.superId
AND A1.prcid = B1.prcid
ORDER BY
    superId,
    prcid