如何获取Oracle中每个组的最大值？

Question

我已经找到了解决此问题的方法，但是，它们似乎与Oracle无关。

我明白了：

我想要一个视图，只显示每个团队中最老的人的信息。所以，我的输出应该是这样的：

PERSON  | TEAM | AGE
Sam     | 1    | 23
Michael | 2    | 21

我怎样才能在Oracle中做到这一点？

Answer 1

一种方法使用keep：

select team, max(age) as age,
       max(person) keep (dense_rank first order by age desc) as person
from t
group by team;

还有其他方法，但根据我的经验，keep效果很好。

Answer 2

以下是没有keep但有row_number()的示例：

with t0 as
(
  select person, team, age,
  row_number() over(partition by team order by age desc) as rn
  from t
)
select person, team, age
from t0
where rn = 1;

Answer 3

select * from table
where (team, age) in (select team, max(age) from table group by team)

Answer 4

select * from (select person,team,age,
       dense_rank() over (partition by team order by age desc) rnk)
       where rnk=1;

Answer 5

使用分析函数返回每个团队中所有年龄最大的人（如果有相同年龄的人需要），只选择一次表，因此比多次引用表的其他解决方案更快：

With MaxAge as (
  Select T.*, Max (Age) Over (Partition by Team) MaxAge
  From Table T
)
Select Person, Team, Age From MaxAge Where Age=MaxAge
;

这也适用于 MySQL/MariaDB。