CREATE TABLE student_course_registrations (student_id VARCHAR)
CREATE TABLE students (student_details VARCHAR, student_id VARCHAR)

What is detail of the student who registered the most number of courses?
SELECT T1.student_details FROM students AS T1 JOIN student_course_registrations AS T2 ON T1.student_id = T2.student_id GROUP BY T1.student_id ORDER BY COUNT(*) DESC LIMIT 1
SELECT "T1"."student_details" FROM "students" AS "T1" JOIN "student_course_registrations" AS "T2" ON "T1"."student_id" = "T2"."student_id" GROUP BY "T1"."student_id" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1