-- Query 27

SELECT
    serveur.numserveur,
    serveur.nomserveur
FROM serveur
WHERE
    NOT EXISTS (
        SELECT *
        FROM facture
        WHERE
            facture.numserveur = serveur.numserveur
            AND facture.numtable = 1
    );

/* == RESULT ==
"numserveur","nomserveur"
50,"Durant Pierre"
51,"Duchemin Paul"
52,"Martin Cathy"
54,"Séré Alain"
*/