SELECT last_name,job_id,e.department_id,department_name FROM employees AS e,departments AS d,locations AS l WHERE e.`department_id`=d.`department_id` AND d.`location_id`=l.`location_id` AND l.city='Toronto' #案例；查询每个国家下的部门个数大于2的国家编号
SELECT country_id ,COUNT(*) FROM locations AS l,departments AS d WHERE l.`location_id`=d.`location_id`
