Joins on multiple tables
SELECT users.id,users.group_id,Approved_Courses.module 
      ,Approved_Courses.order_number , Enrollments.id
FROM 
Users full outer join 
approved_courses
  on users.group_id=approved_courses.group_id
left outer  join Classes 
  on Classes.id=Approved_Courses.group_id and Approved_Courses.module=Classes.module 
left outer join Enrollments
  on Classes.id=Enrollments.class_id 
 and Users.id=Enrollments.staff_id

order by users.id,users.group_id
        ,Approved_Courses.module ,Approved_Courses.order_number