题解
查找所有已经分配部门的员工的last_name和first_name以及dept_no
https://www.nowcoder.com/practice/6d35b1cd593545ab985a68cd86f28671
select employees.last_name ,employees.first_name ,dept_emp.dept_no from dept_emp left join employees on dept_emp.emp_no = employees.emp_no