What is the semester which most student registered in? Show both the name and the id.
create table student_enrolment (semester_id varchar, PRIMARY KEY (semester_id)); create table semesters (semester_name varchar, semester_id varchar, PRIMARY KEY (semester_name))
select t1.semester_name, t1.semester_id from semesters as t1 join student_enrolment as t2 on t1.semester_id = t2.semester_id group by t1.semester_id order by count(*) desc limit 1