select first_name from( select first_name ,row_number() over() rn /*记住原表每行顺序*/ ,rank() over(order by first_name) rk /*order by改变了原表顺序*/ from employees ) frr where rk mod 2 =1 order by rn /*按原表顺序排列*/
select first_name from( select first_name ,row_number() over() rn /*记住原表每行顺序*/ ,rank() over(order by first_name) rk /*order by改变了原表顺序*/ from employees ) frr where rk mod 2 =1 order by rn /*按原表顺序排列*/