如何获得Oracle中每个组的最大值？

Question

I've found some solutions for this problem, however, they don't seem to work with Oracle.

I got this:

I want a view to present only the informations about the oldest person for each team. So, my output should be something like this:

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

How can I do that in Oracle?

Answer 1

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

Answer 2

One method uses keep :

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

There are other methods, but in my experience, keep works quite well.

Answer 3

Here is an example without keep but with row_number() :

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 4

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

Answer 5

Using an Analytic Function returns all people with maximum age per team (needed if there are people with identical ages), selects Table one time only and is thus faster than other solutions that reference Table multiple times:

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

This also works in MySQL/MariaDB.