select sname from dbo.student
where id in (
    select id
	from book bk, borrow br
	where bk.isbn=br.isbn
	and author='Sam Wang'
	) 

select sname from dbo.student
where id in (
    select id
	from book bk, borrow br
	where bk.isbn=br.isbn
	and author='Sherman Chow'
	) 

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