题解 |多表连接
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 last_name,first_name,dept_name from employees e left join dept_emp de on e.emp_no=de.emp_no left join departments d on de.dept_no=d.dept_no