How many clubs are there?
select count(club_id) from club
How many coaches in total?
select count(*) from coach
How many coaches are there from 'AIK' club?
select count(*) from coach as t1 join club as t2 on t1.club_id = t2.club_id where t2.club_name = "AIK"
How many coaches in each club, give the club id, club name and number of coaches.
select t1.club_id, t1.club_name, count(*) from club as t1 join coach as t2 on t1.club_id = t2.club_id group by t1.club_id