SELECT
    CASE
    WHEN s.MiddleName IS NULL THEN FirstName + ' ' + s.LastName
    ELSE FirstName + ' ' + s.MiddleName + ' ' + s.LastName
    END AS [Full Name]
    FROM Students AS s
    LEFT JOIN StudentsSubjects AS ss ON ss.StudentId = s.Id
    WHERE ss.StudentId IS NULL
    ORDER BY [Full Name]