SELECT T1.student_id ,  count(*) FROM students AS T1 JOIN student_course_registrations AS T2 ON T1.student_id = T2.student_id GROUP BY T1.student_id
List the id of students who registered some courses and the number of their registered courses?
SELECT T1.student_id , count ( * ) FROM students AS T1 JOIN student_course_registrations AS T2 ON T1.student_id = T2.student_id GROUP BY T1.student_id
select t1 . student_id , count ( * ) from students as t1 join student_course_registrations as t2 on t1 . student_id = t2 . student_id group by t1 . student_id
List the id of students who registered some courses and the number of their registered courses ?