SELECT
    CASE
        WHEN G.[Grade] < 8 THEN NULL
        ELSE S.[Name]
    END AS StudentName,
    G.[Grade] AS StudentGrade,
    S.[Marks] AS StudentMarks
FROM Students AS S
INNER JOIN Grades AS 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 CAST(S.[Marks] AS VARCHAR(20))
    END ASC;