Give the registration dates of registrations for the course 305.
select registration_date from student_course_registrations where course_id = 305
How about for the course statistics?
select t2.registration_date from courses as t1 join student_course_registrations as t2 on t1.course_id = t2.course_id where t1.course_name = "statistics"
Give the student ids, ordered by the registration date.
select t2.student_id from courses as t1 join student_course_registrations as t2 on t1.course_id = t2.course_id where t1.course_name = "statistics" order by t2.registration_date