SQL Server查询，获取在1字段中具有不同值且在其他字段中具有最大值的记录

我有一个带有一些列的表：

WON   param      |  machine   |    inputdate     |  val
---|-------------|------------|------------------|--------|
18 | PAR.SPTDM.X1|    MM01    | 20/01/2013 12:43 |  2.5   |
18 | PAR.SPTDM.Y1|    MM01    | 20/01/2013 12:43 |  3,4   |
22 | PAR.SPTDM.X1|    MM01    | 22/01/2013 16:10 |  1.2   |
22 | PAR.SPTDM.Y1|    MM01    | 22/01/2013 16:10 |  1.7   |
33 | PAR.SPTDM.X1|    MM03    | 22/01/2013 16:13 |  2.34  |
33 | PAR.SPTDM.Y1|    MM03    | 22/01/2013 16:13 |  2,21  |
27 | PAR.LAS.PWR |    MM10    | 25/01/2013 08:14 |  100.5 |
14 | PAR.LAS.UV  |    MM10    | 18/01/2013 17:27 |  134.8 |
41 | PAR.LAS.UV  |    SLA4    | 27/01/2013 09:14 |  2,1   |
62 | PAR.LAS.UV  |    SLA5    | 27/01/2013 11:15 |  14.6  |

有些行由于我不知道的原因而被复制，这是管理系统的后端。值列也是字符串，需要转换为数字

数据库是只读的，我想根据以下几个条件将数据拉入Excel工作表：

按机器和参数分组 参数上的筛选器：仅“PAR.SPTDM.%” 机器上的过滤器：仅“MM%” 忽略带有逗号的val，将其余的转换为数字 使用以下查询时，此操作不会出现任何问题：

SELECT DISTINCT t1.param, t1.machine, cast(t1.val as float), t1.inputdate
FROM dbbackend t1
WHERE (t1.machine Like 'MM%')
    AND (t1.param Like 'PAR.SPTDM.%')
    AND (t1.val<>'') And (t1.val not Like '%,%')

但这给了我数据集中不存在的val，正确的machine/param/inputdate，但val是错误的

下一次尝试是

SELECT DISTINCT t1.param, t1.machine, cast(t1.val as float), t1.inputdate
FROM dbbackend t1
WHERE t1.WON IN
    (
    SELECT latestrec.WON FROM (
        SELECT DISTINCT max(t2.WON), t2.param, t2.machine, max(t2.inputdate)
        FROM dbbackend t2
        WHERE (t2.machine Like 'MM%')
            AND (t2.param Like 'PAR.SPTDM.%')
            AND (t2.val<>'') And (t2.val not Like '%,%')
            GROUP BY machine, param
        ) as latestrec
    )

但这是行不通的，Query女士告诉我

无法添加该表

那么，有人能告诉我为什么第一次调用得到错误的值，为什么第二次调用不起作用，或者正确的方法是什么？我还怀疑MS query会被嵌套的子查询绊倒：//

您可以使用ROW\u NUMBER函数尝试此CTE：

WITH x AS (SELECT t1.param, 
                t1.machine, 
                Cast(t1.val AS FLOAT) AS val, 
                t1.inputdate, 
                RN=Row_number() 
                     OVER( 
                       partition BY t1.machine, t1.param 
                       ORDER BY t1.inputdate DESC) 
         FROM   dbbackend t1 
         WHERE  ( t1.machine LIKE 'MM%' ) 
                AND ( t1.param LIKE 'PAR.SPTDM.%' ) 
                AND ( t1.val <> '' ) 
                AND ( t1.val NOT LIKE '%,%' )) 
SELECT param, 
       machine, 
       val, 
       inputdate 
FROM   x 
WHERE  rn = 1 

您可以使用ROW_NUMBER函数尝试此CTE：

WITH x AS (SELECT t1.param, 
                t1.machine, 
                Cast(t1.val AS FLOAT) AS val, 
                t1.inputdate, 
                RN=Row_number() 
                     OVER( 
                       partition BY t1.machine, t1.param 
                       ORDER BY t1.inputdate DESC) 
         FROM   dbbackend t1 
         WHERE  ( t1.machine LIKE 'MM%' ) 
                AND ( t1.param LIKE 'PAR.SPTDM.%' ) 
                AND ( t1.val <> '' ) 
                AND ( t1.val NOT LIKE '%,%' )) 
SELECT param, 
       machine, 
       val, 
       inputdate 
FROM   x 
WHERE  rn = 1