use library;
select sname from dbo.student
where id in (
   select br.id
   from dbo.book bk,                   --book
        dbo.borrow br
   where bk.isbn = br.isbn
   and   author = 'Sam Wang'
   --and author != 'Sherman Chow'
   )
   --This query fails to further limit the selection
   --if we drop the commented line.