How many states that have some college students playing in the mid position but not in the goalie position.
select count(*) from (select t1.state from college as t1 join tryout as t2 on t1.cname = t2.cname where t2.ppos = 'mid' except select t1.state from college as t1 join tryout as t2 on t1.cname = t2.cname where t2.ppos = 'goalie')