Database: e_learning

Question: Find the personal names of students not enrolled in any course.
SQL: SELECT personal_name FROM Students EXCEPT SELECT T1.personal_name FROM Students AS T1 JOIN Student_Course_Enrolment AS T2 ON T1.student_id  =  T2.student_id

Question: How many students did not have any course enrollment?
SQL: SELECT count(*) FROM Students WHERE student_id NOT IN (SELECT student_id FROM Student_Course_Enrolment)

Question: Find the common login name of course authors and students.
SQL: SELECT login_name FROM Course_Authors_and_Tutors INTERSECT SELECT login_name FROM Students