select distinct ID
from dbo.XXX

Select distinct name
from dbo.XXX

Select distinct age
from dbo.XXX

Select ID, count(id) as [ID_Recurrence]
from dbo.XXX
group by ID

Select Age, count(age) as [Age_Recurrence]
from dbo.XXX
group by Age

Select Name, count(name) as [Name_Recurrence]
from dbo.XXX
group by Name

select COUNT(distinct id) uniqueIDCount
from dbo.XXX

SELECT DISTINCT ID FROM SomeTable
SELECT DISTINCT ID , SCORE FROM SomeTable

select t.id, t.player_name, t.team
from tablename t
join (select team, min(id) as minid from tablename group by team) x
on x.team = t.team and x.minid = t.id