use library;
select sname from dbo.student
where id in (
   select br.id
   from dbo.book bk,
        dbo.borrow br
   where bk.isbn = br.isbn
   and   author = 'Sam Wang')
except
select sname
from dbo.student
where id in (
   select id
   from dbo.book bk,
        dbo.borrow br
   where bk.isbn = br.isbn
   and author = 'Sherman Chow')