What schools have players that tried out for goalies?
select cname from tryout where ppos = 'goalie'
What schools have players that tried out for the mid position?
select cname from tryout where ppos = 'mid'
What are the names of schools that fit into the latter category but not the former?
select cname from tryout where ppos = 'mid' except select cname from tryout where ppos = 'goalie'