oracle rownum對排序的影響

1. 標準的rownum分頁查詢使用方法：

    select *
      from (select c.*, rownum rn from content c)
     where rn >= 1
       and rn <= 5

    2. 可是若是, 加上order by addtime 排序則數據顯示不正確

    select *
      from (select c.*, rownum rn from content c order by addtime)
     where rn >= 1
       and rn <= 5

    解決方法，再加一層查詢，則能夠解決，

    select *
      from (select rownum rn, t.*
              from (select title, addtime from content order by addtime desc) t)
     where rn >= 1
       and rn <= 5

    若是要考慮到效率的問題，上面的還能夠優化成（主要二者區別）

    select *
      from (select rownum rn, t.*
              from (select title, addtime from content order by addtime desc) t
             where rownum <= 10)
     where rn >= 3