题解查找所有员工
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 a1.last_name,a1.first_name,a2.dept_name from(select e.last_name,e.first_name,d.dept_no from employees e left join dept_emp d on e.emp_no=d.emp_no)a1 left join departments a2 on a1.dept_no = a2.dept_no