รหัสสถานะลูกค้าใดมีจำนวนลูกค้าน้อยที่สุด?ไม่จำเป็นต้องใช้ทุกตาราง
Which customer status code has least number of customers?It is not neccessary to use all the tables.
 lessons:  lesson_id [ number]  customer_id [ number]  lesson_status_code [ text]  staff_id [ number]  vehicle_id [ number]  lesson_date [ time]  lesson_time [ text]  price [ number] 
SELECT customer_status_code FROM customers GROUP BY customer_status_code ORDER BY COUNT(*) LIMIT 1