求不重复的字段并返回最新日期的SQL方法

有下面的一段原数据：

KS_Date	KS_MetalName	KS_TopLimit	KS_BottomLimit	KS_Average	KS_Change
2011-12-14 00:00:00.000	a	100	10	55	54
2011-12-14 00:00:00.000	b	1	1	2	2
2011-12-14 00:00:00.000	c	1	1	10	1
2011-12-14 00:00:00.000	d	1	1	1	1
2011-12-14 00:00:00.000	e	1	1	1	1
2011-12-14 00:00:00.000	f	1	1	1	1
2011-12-14 00:00:00.000	g	1	1	1	1
2011-12-15 00:00:00.000	a	10	10	10	-45
2011-12-16 00:00:00.000	b	2	10	6	4
2011-12-16 00:00:00.000	c	2653	2001	2327	2317
2011-12-16 00:00:00.000	d	300	10	155	154
2011-12-16 00:00:00.000	e	200	100	150	149
2011-12-16 00:00:00.000	f	500	300	400	399
2011-12-16 00:00:00.000	g	5000	200	2600	2599
2011-12-23 00:00:00.000	a	20	10	15	5
2011-12-24	a	22	3	3	3
NULL	NULL	NULL	NULL	NULL	NULL

1、求最新的日期并且KS_MetalName不重复

SELECT     MAX(KS_Date) AS 最新日期, KS_MetalName
FROM         KS_U_SpotPrice
GROUP BY KS_MetalName

缺陷是无法返回多行记录，只能返回最多现行：KS_Date和KS_MetalName不能满足我们的要求

2、现在变通方法如下：

SELECT     KS_Date, KS_MetalName, KS_TopLimit, KS_BottomLimit, KS_Average, KS_Change
FROM         KS_U_SpotPrice
WHERE     (KS_Date IN
                          (SELECT     MAX(KS_Date) AS AS最新日期
                            FROM          KS_U_SpotPrice AS TempTable
                            GROUP BY KS_MetalName))
ORDER BY KS_MetalName

突然间发现上面这种方法也不能满足要求 ,但是下面的方法保证没有问题：

SELECT     ID, KS_Date, KS_MetalName, KS_TopLimit, KS_BottomLimit, did, username, userleavel
FROM         test AS a
WHERE     (KS_Date IN
                          (SELECT     MAX(KS_Date) AS Expr1
                            FROM          test AS b
                            WHERE      (a.KS_MetalName = KS_MetalName)))
ORDER BY KS_MetalName

3、如果要是求今天最新的日期的返回值方法如下：

select KS_Date,KS_MetalName,KS_TopLimit,KS_BottomLimit,KS_Average,KS_Change
 from KS_U_SpotPrice
 where  (DATEDIFF("d",KS_Date,GETDATE())=0) 
order by KS_MetalName ASC