1.可用左连接方法来做
elect e.last_name,e.first_name,d.dept_no
from dept_emp d left join employees e on d.emp_no=e.emp_no;
2.可用where 来做
elect e.last_name,e.first_name,d.dept_no
from dept_emp d ,employees e
where d.emp_no=e.emp_no;