Steve Johnson รองรับลูกค้าได้กี่ราย?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
How many customers does Steve Johnson support?It is not neccessary to use all the tables.
 employees:  (id [ VARCHAR ] first_name [ VARCHAR ] last_name [ VARCHAR) ]
SELECT COUNT(*) FROM employees AS T1 JOIN customers AS T2 ON T2.support_rep_id = T1.id WHERE T1.first_name = "Steve" AND T1.last_name = "Johnson"