* SOL 2
* 1 STUDENT
iStudentId = NNNN
* ALL STUDENTS
iStudentId = NULL
WHERE courses.iid = m.iCourseId AND (m.iStudentId IS NULL OR students.iid = m.iStudentId)

* SOL 1
* 1 STUDENT
wExp = "courses.iid = m.iCourseId AND students.iid = m.iStudentId"
* ALL STUDENTS
wExp = "courses.iid = m.iCourseId"
WHERE &wExp

* SOL 3
* 1 STUDENT
sStudentId = STR(NNNN)
* ALL STUDENTS
sStudentId = '%'
WHERE courses.iid = m.iCourseId AND STR(students.iid) LIKE m.sStudentId