SQL Server：只有GROUP BY中的最后一项 [英] SQL Server: Only last entry in GROUP BY

问题描述

  id |在MSSQL2005中有以下表格
 business_key |结果
 1 | 1 | 0 
 2 | 1 | 1 
 3 | 2 | 1 
 4 | 3 | 1 
 5 | 4 | 1 
 6 | 4 | 0 
  

现在我想根据business_key返回具有最高id的完整条目。
所以我的预期结果是：

  business_key |结果
 1 | 1 
 2 | 1 
 3 | 1 
 4 | 0 
  

我敢打赌，有一种方法可以实现这一点，我只是无法在。

解决方案

另一种解决方案可以提供更好的性能（测试两种​​方式并检查执行计划） p>

  SELECT 
 T1.id，
 T1.business_key，
 T1.result 
 FROM 
 dbo.My_Table T1 
 LEFT OUTER JOIN dbo.My_Table T2 ON 
 T2.business_key = T1.business_key AND 
 T2.id> T1.id 
 WHERE 
 T2.id IS NULL 
  

此查询假定该ID是一个唯一值（至少对于任何给定的business_key）并且它被设置为NOT NULL。

I have the following table in MSSQL2005

id | business_key | result
1 | 1 | 0
2 | 1 | 1
3 | 2 | 1
4 | 3 | 1
5 | 4 | 1
6 | 4 | 0

And now i want to group based on the business_key returning the complete entry with the highest id. So my expected result is:

business_key | result
1 | 1
2 | 1
3 | 1
4 | 0

I bet that there is a way to achieve that, i just can't see it at the moment.

解决方案

An alternative solution, which may give you better performance (test both ways and check the execution plans):

SELECT
     T1.id,
     T1.business_key,
     T1.result
FROM
     dbo.My_Table T1
LEFT OUTER JOIN dbo.My_Table T2 ON
     T2.business_key = T1.business_key AND
     T2.id > T1.id
WHERE
     T2.id IS NULL

This query assumes that the ID is a unique value (at least for any given business_key) and that it is set to NOT NULL.

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