SELECT 
    CASE WHEN G.grade >= 8 
        THEN S.name
        ELSE "NULL"
    END,
    G.grade, 
    S.marks 
FROM STUDENTS as S
JOIN GRADES as G ON 
    S.marks >= G.min_mark AND 
    S.marks <= G.max_mark
ORDER BY 
    G.grade DESC, 
    S.name ASC, 
    S.marks;