题解 | #查找所有员工的last_name和first_name以及对应部门编号dept_no#

先把两表连接起来, 由于题目说明了要把没有分配到的员工也一并输出,所以在此我们选择left join

select e.*, de.dept_no
from employees as e
left join dept_emp as de
on e.emp_no = de.emp_no

最后再选择first_name, last_name和dept_no

select first_name, last_name, dept_no
from (
    select e.*, de.dept_no
    from employees as e
    left join dept_emp as de
    on e.emp_no = de.emp_no
) t1