[求助]怎么从产品表中获取每一类的前N个产品

[edgesun]

现有两个表：产品类别表[category]，产品表[products]

表结构：

产品类别表[category]：cate_id, cate_name

产品表[products]：p_id, p_name, cate_id

要求：从products表取得category中各类别的前（或后）N个产品。

我只会比较笨的做法：先从category中查询各字段id，然后循环从products表中查询，如下：


Set Rs=CONN.Execute("Select cate_id From category")
Do While Not Rs.Eof
Set Rs2=CONN.Execute("Select Top 5 * From products Where cate_id="&Rs("cate_id"))
Do While Not Rs2.Eof
...............
Loop
Loop


问：怎么用一个SQL语句，实现以上功能？

知道有group by、having、等查询方法，但不知道怎么实现，也不知道能否实现。忘高手指点。

谢谢了先！

[guguda2008]

DECLARE @N INT
SELECT @N=3
SELECT * FROM (
SELECT *,ROW_NUMBER() OVER(PARTITION BY CATE_ID ORDER BY P_ID) AS NID FROM PRODUCTS
) T WHERE NID<=@N

[王向飞]

---------------------------------
--  Author: liangCK 小梁
--  Title : 查每个分组前N条记录
--  Date  : 2008-11-13 17:19:23
---------------------------------

--> 生成测试数据: #T
IF OBJECT_ID('tempdb.dbo.#T') IS NOT NULL DROP TABLE #T
CREATE TABLE #T (ID VARCHAR(3),GID INT,Author VARCHAR(29),Title VARCHAR(39),Date DATETIME)
INSERT INTO #T
SELECT '001',1,'邹建','深入浅出SQLServer2005开发管理与应用实例','2008-05-10' UNION ALL
SELECT '002',1,'胡百敬','SQLServer2005性能调校','2008-03-22' UNION ALL
SELECT '003',1,'格罗夫Groff.J.R.','SQL完全手册','2009-07-01' UNION ALL
SELECT '004',1,'KalenDelaney','SQLServer2005技术内幕存储引擎','2008-08-01' UNION ALL
SELECT '005',2,'Alex.Kriegel.Boris.M.Trukhnov','SQL宝典','2007-10-05' UNION ALL
SELECT '006',2,'飞思科技产品研发中心','SQLServer2000高级管理与开发','2007-09-10' UNION ALL
SELECT '007',2,'胡百敬','SQLServer2005数据库开发详解','2008-06-15' UNION ALL
SELECT '008',3,'陈浩奎','SQLServer2000存储过程与XML编程','2005-09-01' UNION ALL
SELECT '009',3,'赵松涛','SQLServer2005系统管理实录','2008-10-01' UNION ALL
SELECT '010',3,'黄占涛','SQL技术手册','2006-01-01'

--SQL查询如下:

--按GID分组,查每个分组中Date最新的前2条记录


--1.字段ID唯一时:
SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 2 ID FROM #T WHERE GID=T.GID ORDER BY Date DESC)

--2.如果ID不唯一时:
SELECT * FROM #T AS T WHERE 2>(SELECT COUNT(*) FROM #T WHERE GID=T.GID AND Date>T.Date)

--SQL Server 2005 使用新方法

--3.使用ROW_NUMBER()进行排位分组
SELECT ID,GID,Author,Title,Date
FROM
(
   SELECT rid=ROW_NUMBER() OVER(PARTITION BY GID ORDER BY Date DESC),*
   FROM #T
) AS T
WHERE rid<=2

--4.使用APPLY
SELECT DISTINCT b.*
FROM #T AS a
CROSS APPLY
(
    SELECT TOP(2) * FROM #T WHERE a.GID=GID ORDER BY Date DESC
) AS b


--结果
/*

ID   GID         Author                        Title                                   Date
---- ----------- ----------------------------- --------------------------------------- -----------------------
003  1           格罗夫Groff.J.R.                 SQL完全手册                                 2009-07-01 00:00:00.000
004  1           KalenDelaney                  SQLServer2005技术内幕存储引擎                   2008-08-01 00:00:00.000
005  2           Alex.Kriegel.Boris.M.Trukhnov SQL宝典                                   2007-10-05 00:00:00.000
007  2           胡百敬                           SQLServer2005数据库开发详解                    2008-06-15 00:00:00.000
009  3           赵松涛                           SQLServer2005系统管理实录                     2008-10-01 00:00:00.000
010  3           黄占涛                           SQL技术手册                                 2006-01-01 00:00:00.000

(6 行受影响)
*/



参考参考这个 看看满足你的需求吗

[edgesun]

谢谢楼上两位。俺用的只是ACCESS，所以二楼的SQL正是我需要的。
--1.字段ID唯一时:
SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 2 ID FROM #T WHERE GID=T.GID ORDER BY Date DESC)

--2.如果ID不唯一时:
SELECT * FROM #T AS T WHERE 2>(SELECT COUNT(*) FROM #T WHERE GID=T.GID AND Date>T.Date)

再次感谢两位