SQL查询/子查询需要帮助

Question

我想从测试信息表中获取的SQL Server 2005上的最后10序列号的列表，我想是这样的：

SELECT DISTINCT TOP (10) Serial, DateTime 
FROM [Test].[dbo].[TestInfo] 
WHERE (TestedBy = 'JSMITH') ORDER BY DateTime DESC 

返回重复序列号：

+---------+-------------------------+ 
| Serial | DateTime    | 
+-----------------------------------+ 
| 1114048 | 2011-03-16 11:03:14.000 | 
| 1617683 | 2011-03-11 15:07:29.000 | 
| 1617683 | 2011-03-11 15:07:27.000 | 
| 1617683 | 2011-03-11 15:07:26.000 | 
| 1617683 | 2011-03-10 13:16:04.000 | 
| 1617683 | 2011-03-10 13:15:35.000 | 
| 1617683 | 2011-03-10 13:15:30.000 | 
| 1617683 | 2011-03-07 13:42:48.000 | 
| 1617683 | 2011-03-07 13:40:32.000 | 
| 1617683 | 2011-03-07 13:37:58.000 | 
+---------+-------------------------+ 

有没有一种方法，或者使用查询或子查询来获取最后的10个序列号没有重复？

Answer 1

select top (10) Serial, Max(DateTime) 
from [Test].[dbo].[TestInfo] 
where (TestedBy = 'JSMITH') 
group by Serial 
order by Max(DateTime) desc 

Answer 2

它返回重复行，因为每行的日期时间不同。 如果您只需要串行字段，则必须在查询中只写入“串行”字段。

Answer 3

SELECT TOP 10 
    * 
FROM (SELECT 
     Serial, 
     MAX(DateTime) AS DateTime 
     FROM [Test].[dbo].[TestInfo] 
     WHERE (TestedBy = 'JSMITH') 
     GROUP BY Serial) q1 
ORDER BY q1.DateTime DESC 

Answer 4

大概是这样的：

SELECT DISTINCT TOP (10) Serial, DateTime 
FROM (
    SELECT Serial, MAX(DateTime) AS DateTime 
    FROM [Test].[dbo].[TestInfo] 
    WHERE (TestedBy = 'JSMITH') 
    GROUP BY Serial 
) AS sub 
ORDER BY DateTime DESC