SELECT     pdbs.*
FROM       pdbs JOIN (
  SELECT   PdbId, ResName, COUNT(*) as c
  FROM     pdbs
  GROUP BY PdbId, ResName
  HAVING   c >= 2
) AS       counter
ON         pdbs.PdbId   = counter.PdbId
AND        pdbs.ResName = counter.ResName
WHERE      pdbs.ResName = 'CL'
;