利用union
查找所有员工的last_name和first_name以及对应部门编号dept_no
https://www.nowcoder.com/practice/dbfafafb2ee2482aa390645abd4463bf
select e.last_name,e.first_name,d.dept_no from employees as e join dept_emp as d on e.emp_no=d.emp_no union select last_name,first_name,null as dept_no from employees where emp_no not in (select emp_no from dept_emp);
投递水滴等公司10个岗位 >