解题思路： 先用窗口函数选取职工编号、姓名、序号等信息，然后再按条件筛选即可

```select t.first_name
from (select emp_no,first_name,rank()over(order by first_name ASC) as rk from employees) 
as t
where t.rk MOD 2 = 1
order by t.emp_no asc