SELECT
    CASE
        WHEN g.grade < 8 THEN NULL
        ELSE s.name
    END AS student_name,
    g.grade,
    s.marks
FROM students s
JOIN
    grades g
ON
    s.marks BETWEEN g.min_mark AND g.max_mark
ORDER BY
    g.grade DESC,
    CASE
        WHEN g.grade >= 8 THEN s.name
        ELSE s.marks
    END ASC;