题解 | 查找所有员工的信息（左关联）
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
a.last_name as last_name,
a.first_name as first_name,
b.dept_no as dept_no
from
(
select
*
from
employees
) a
left join (
select
*
from
dept_emp
) b on a.emp_no = b.emp_no
