美丽的CTE

with ranked as (select emp_no, first_name, row_number() over ( order by first_name) as rn from employees),

original_order as (select emp_no, first_name from employees order by emp_no),

extracted as (select emp_no, first_name from ranked where rn = 1 or rn % 2 = 1),

final as (select distinct o.emp_no, o.first_name as orifirst, ex.first_name as exfirst from original_order o, extracted ex where o.first_name = ex.first_name order by o.emp_no)

select exfirst from final