SELECT
    ETU.Nom,
    ETU.Prenom,
    SUM(MAT.CoeffMat * AVG(EVA.Note)) / SUM(MAT.CoeffMat) AS moyenne
FROM
    ETUDIANT AS ETU
JOIN
    EVALUER AS EVA ON EVA.NumEtudiant = ETU.NumEtudiant
JOIN
    MATIERE AS MAT ON MAT.CodeMat = EVA.CodeMat
GROUP BY
    ETU.Nom,
    ETU.Prenom;