本文介绍了为每个 ID 获取最大值的简单查询的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
好的，我有一张这样的桌子:
OK I have a table like this:
ID Signal Station OwnerID
111 -120 Home 1
111 -130 Car 1
111 -135 Work 2
222 -98 Home 2
222 -95 Work 1
222 -103 Work 2
这一切都是为了同一天.我只需要查询返回每个 ID 的最大信号:
This is all for the same day. I just need the Query to return the max signal for each ID:
ID Signal Station OwnerID
111 -120 Home 1
222 -95 Work 1
我尝试使用 MAX() 并且聚合混乱，因为每个记录的 Station 和 OwnerID 都不同.我需要加入吗?
I tried using MAX() and the aggregation messes up with the Station and OwnerID being different for each record. Do I need to do a JOIN?
推荐答案
类似这样的事情?将您的表格与自身连接起来，并排除发现较高信号的行.
Something like this? Join your table with itself, and exclude the rows for which a higher signal was found.
select cur.id, cur.signal, cur.station, cur.ownerid
from yourtable cur
where not exists (
select *
from yourtable high
where high.id = cur.id
and high.signal > cur.signal
)
这将为每个最高信号列出一行，因此每个 id 可能有多行.
This would list one row for each highest signal, so there might be multiple rows per id.
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