How many students are enrolled in "French"?
select count(*) from courses as t1 join student_course_enrolment as t2 on t1.course_id = t2.course_id where t1.course_name = "French"
Okay, how many students are enrolled in "AI"?
select count(*) from courses as t1 join student_course_enrolment as t2 on t1.course_id = t2.course_id where t1.course_name = "AI"
So what are the names of the courses that have exactly 1 student enrollment?
select t1.course_name from courses as t1 join student_course_enrolment as t2 on t1.course_id = t2.course_id group by t1.course_name having count(*) = 1