To calculate the students' end of year mark in school data base with one query

SELECT
     student.snumber AS 'Student Number',
     student.name AS 'First Name',
     student.lastname AS 'Last Name',
     SUM( smarks.smark ) AS 'Total Mark',
     COUNT( * ) AS 'Total Lesson',
     (SUM( smarks.smark ) / COUNT( * )) AS 'Marks End Of Year'
FROM
     students AS student
  LEFT JOIN
     smarks
   ON
     smarks.student_id = student.id
  LEFT JOIN
     lessons AS lesson
   ON
     lesson.lesson_id = smarks.lesson_id
GROUP BY
   student.snumber
ORDER BY
   'Marks End Of Year' DESC