SELECT DISTINCT nomserv, nomproj,
(SELECT SUM(duree) FROM basetd.travail WHERE travail.nuproj =projet.nuproj) AS duree
FROM basetd.service, basetd.projet, basetd.concerne, basetd.travail
WHERE service.nuserv = concerne.nuserv AND concerne.nuproj = projet.nuproj
ORDER BY nomserv, duree;