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问题描述
我在 MSSQL2005 中有下表
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
现在我想根据 business_key 进行分组，返回具有最高 ID 的完整条目.所以我的预期结果是:
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
我敢打赌有一种方法可以实现这一目标，但目前我看不到.
I bet that there is a way to achieve that, i just can't see it at the moment.
推荐答案
另一种解决方案，它可能会给您带来更好的性能(测试两种方式并检查执行计划):
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
这个查询假设 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.
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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