所有员工的last_name和first_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 last_name,first_name,dept_name from employees e left join dept_emp d on e.emp_no=d.emp_no left join departments t on d.dept_no=t.dept_no
