# 子查询：按照first_name进行升序排序并标明序号
# 总查询，把奇数序号的取出来
select 
    a.first_name as first
from
(select
    *,
    rank() over(order by first_name) as ranks
from
    employees) a
where
    mod(a.ranks,2) = 1
order by 
    a.emp_no