SQL - Confusing Query
photoID (INT), setID (INT)....
18900 , 234 , ...
18901 , 234 , ...
18902 , 234 , ...
18903 , 249 , ...
18904 , 249 , ...
18905 , 249 , ...

photoID (INT), keywordID (INT)
18900 , 12
18900 , 21
18901 , 17
18905 , 26
18905 , 10

SELECT X.photoID FROM photos X
INNER JOIN
(SELECT DISTINCT P.setID FROM
photos P
LEFT OUTER JOIN (SELECT K.photoID, COUNT(*) C FROM photoKeyword K GROUP BY K.photoID) KC ON KC.photoID = P.photoID
GROUP BY P.setID
HAVING SUM (KC.C) < 1) Y ON X.setID = Y.SetID

SELECT photoID
     , setID
FROM photos
WHERE photoID NOT IN
      ( SELECT photoID
        FROM photoKeyword
      )
  AND setID =
      ( SELECT setID
        FROM photos
        WHERE photoID NOT IN
             ( SELECT photoID
               FROM photoKeyword
             )
        ORDER BY setID
        LIMIT 1
      )

select
      p.PhotoID,
      p.SetID
   from
      Photos p
         LEFT JOIN photoKeyword pkey
            on p.PhotoID = pkey.PhotoID
   where
      pkey.PhotoID = null

SELECT p.setID, GROUP_CONCAT(p.photoID ORDER BY p.photoID) AS photoIDs
  FROM photos p
  JOIN photoKeyword k USING (photoID)
 WHERE k.photoID IS NULL
 GROUP BY 1
 LIMIT 1