SELECT COUNT(*) AS nbr_doublon, champ1, champ2, champ3 FROM TABLE GROUP BY champ1, champ2, champ3 HAVING COUNT(*) > 1
SELECT DISTINCT * FROM TABLE t1 WHERE EXISTS ( SELECT * FROM TABLE t2 WHERE t1.ID <> t2.ID AND t1.champ1 = t2.champ1 AND t1.champ2 = t2.champ2 AND t1.champ3 = t2.champ3 )