ค้นหาเมืองที่มีร้านค้ามากที่สุด ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
Find the city with the most number of stores.It is not neccessary to use all the tables.
 district:  (headquartered_city [ VARCHAR ] district_id [ VARCHAR) ]
SELECT t3.headquartered_city FROM store AS t1 JOIN store_district AS t2 ON t1.store_id = t2.store_id JOIN district AS t3 ON t2.district_id = t3.district_id GROUP BY t3.headquartered_city ORDER BY COUNT(*) DESC LIMIT 1