select first_name 
from employees 
where first_name in (
    select first_name from (
        select first_name,(@i:=@i+1) n from (
            select first_name 
            from employees 
            order by first_name)t1,(select @i:=0)t )t2 where n%2=1 )

我就觉得这题超级莎比。。。。