step1：按driver_id相等的条件，将order_info_tb左连接driver_tb;

step2：按city_id相等的条件，左连接ciity_tb；

step3：按driver_id分组，统计不重复的订单数量；

step4：只显示订单量大于1的司机信息。

select city_name, driver_id, COUNT(DISTINCT order_id) as order_num

FROM(

SELECT a.driver_id, city_name, order_id FROM order_info_tb a

LEFT JOIN driver_tb b

ON a.driver_id=b.driver_id

LEFT JOIN city_tb c

ON b.city_id=c.city_id)t

GROUP BY driver_id

HAVING order_num>1

ORDER BY driver_id;