Question

I have the following table:

  'committee' table  commname    profname ======================== commA       bill commA       jack commA       piper commB       bill commB       piper  

and I am trying to find the professors who are in every committee that ‘piper’ is in (answer should be piper and bill):

I have the following SQL division query but it’s wrong and I can’t figure out where the problem is (doesn’t return bill, just piper):

  select b.profname from committee b where not exists   (select commname from committee a where profname = 'piper' and not exists   (select commname from committee where a.profname=b.profname ))  

Can somebody help me with this one? Thanks,

Answer 1

Your innermost select isn’t using anything from itself in its where clause, so it’s always finding something for piper. Try

select distinct b.profname from committee b where not exists (     select commname from committee a     where a.profname = 'piper' and not exists  (         select commname from committee c         where c.profname=b.profname and c.commname=a.commname     ) );