Find the average height of the players who belong to the college called 'Yale University'.
SELECT avg(T1.height) FROM player AS T1 JOIN player_college AS T2 ON T1.player_id  =  T2.player_id JOIN college AS T3 ON T3.college_id  =  T2.college_id WHERE T3.name_full  =  'Yale University';
average height = AVG(height); players who belong to = JOIN on player_id and college_id; college called 'Yale University' refers to WHERE college.name_full = 'Yale University';