with employees_rank as (
    select 
        *,
        row_number() over(order by first_name) as rn
    from 
        employees
)

select
    e.first_name as first
from 
    employees as e
left join 
    employees_rank as e_r
on 
    e.first_name = e_r.first_name
where 
    mod(e_r.rn,2) = 1