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,一段不错的代码,留存备用,转自(loveyuki.com),感谢。
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
下面是我用到了一个产品分类表中,superId是大分类,prcid是产品分类。能用SQL完成的功能就要尽量用SQL语句来完成,这既简洁又高效。
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