Table schema:
CREATE TABLE courses (course_name VARCHAR, course_id VARCHAR); CREATE TABLE student_course_registrations (course_Id VARCHAR)

Question: which course has most number of registered students?
SQL: SELECT T1.course_name FROM courses AS T1 JOIN student_course_registrations AS T2 ON T1.course_id = T2.course_Id GROUP BY T1.course_id ORDER BY COUNT(*) DESC LIMIT 1