Course_enrolments(student, course, mark, grade, ...)
Courses(id, subject, semester, homepage)
People(id, family, given, title, name, ..., birthday)
Program_enrolments(id, student, semester, program, wam, ...)
Students(id, stype)
Subjects(id, code, name, longname, uoc, offeredby, ...)

create view EnrolmentCounts as
 select s.code, c.semester, count(e.student) as nstudes
   from Courses c join Subjects s on c.subject=s.id
        join Course_enrolments e on e.course = c.id
  group by s.code, c.semester;