SELECT c1.nom,c1.prenom, c1.adresse, c1.ville, c1.telbureau1, c1.idcontact
FROM contact c1
LEFT OUTER JOIN contact c2 ON c2.idcontact != c1.idcontact AND c2.nom = c1.nom AND c2.ville= c1.ville
WHERE c2.idcontact IS NOT NULL
order by nom, ville