Show all the positions of the players.
select position from player
How many unique positions are there?
select count (distinct position) from player
How many players are there for each of them?
select position, count (*) from player group by position
What is the average points of all players?
select avg(points) from player
What are the positions of the players with average number of points scored by players of that position bigger than 20?
select position from player group by name having avg(points) >= 20