Tell me how many course enrollments there are?
select count(*) from student_course_enrolment
Tell me how many there are for the student named Jewel?
select count(*) from student_course_enrolment as t1 join students as t2 on t1.student_id = t2.student_id where t2.personal_name = "Jewel"
Tell me the student ID and login name of the student with the most course enrollments.
select t1.student_id, t2.login_name from student_course_enrolment as t1 join students as t2 on t1.student_id = t2.student_id group by t1.student_id order by count(*) desc limit 1