例：
方法一：
select e.last_name,d.department_name,l.city from employees e inner join departments d on e.department_id = d.department_id inner join locations l on d.location_id = l.location_id where e.employee_id = 202;
方法二：在内连接中使用using子句定义等值连接
select e.last_name,d.department_name,l.city from employees e inner join departments d using(department_id) inner join locations l using(location_id) where e.employee_id = 202;