city_code ของเมืองที่นักเรียนอาศัยอยู่มากที่สุดคืออะไร?ไม่จำเป็นต้องใช้ตารางทั้งหมด
What is the city_code of the city that the most students live in?It is not neccessary to use all the tables.
 voting_record:  stuid [ number]  registration_date [ text]  election_cycle [ text]  president_vote [ number]  vice_president_vote [ number]  secretary_vote [ number]  treasurer_vote [ number]  class_president_vote [ number]  class_senator_vote [ number] 
SELECT city_code FROM student GROUP BY city_code ORDER BY COUNT(*) DESC LIMIT 1