查找员工的last_name
查找所有员工的last_name和first_name以及对应的dept_name
https://www.nowcoder.com/practice/5a7975fabe1146329cee4f670c27ad55
select e.last_name,e.first_name,d2.dept_name from employees e left join dept_emp d1 on e.emp_no = d1.emp_no left join departments d2 on d1.dept_no = d2.dept_no
通过三表左连接