what is worng with my solution?

SELECT CASE WHEN G.Grade < 8 THEN NULL ELSE S.Name END AS name, G.Grade, S.Marks

FROM Students S JOIN Grades G ON FLOOR(S.Marks/10)+1 = G.Grade ORDER BY G.Grade DESC, CASE WHEN G.Grade >= 8 THEN S.Name ELSE NULL END ASC,

CASE
    WHEN G.Grade < 8 THEN S.Marks
    ELSE NULL
END ASC;