D.id = 1, open=true, D.CID = 2
D.id = 2, open=true, D.CID = 3
D.id = 3, open=true, D.CID = 3
D.id = 4, open=true, D.CID = 4

C.id = 2, A.id = 3, B.id = 5
C.id = 3, A.id = 3, B.id = 5
C.id = 4, A.id = 4, B.id = 6

1. count = 3  A.id = 3  B.id = 5
2. count = 1  A.id = 4  B.id = 6

For each entry i in tuple Table AB
   for each entry j in Table C
      for each entry k in Table D
          if j.AID AND j.BID equal to i.AID and i.BID
              And if k.CID = j.id
                 Then returnHash[i] = returnHash[i] + 1

SELECT
  COUNT(*),
  c.aid,
  c.bid
FROM
  d INNER JOIN c
ON
  d.cid = c.id
WHERE
  d.open
GROUP BY
  c.aid,
  c.bid;