【思路】-分頁-雙top分頁算法的原理

描述：實現分頁的一種算法

大體過程：訪客訪問不一樣的分頁，爲這個當前頁生成動態的查詢SQL，而後送到數據庫中執行

輸入：總條數，每頁多少條，第幾頁，查詢的SQL，排序的字段

注意：傳入的排序字段須要構成惟一記錄，這就意味着不能單獨的使用SortOrder這個單獨排序

字段反轉：SortOrder asc,PostID desc；反轉以後是 SortOrder desc,PostID asc；

實現過程

訪問第一頁

訪問最後一頁

訪問前半數分頁

訪問後半數分頁

100條數據 每頁顯示4條 按照ID降序 排序

當取第一頁時：直接對全部數據降序取出前4條

當取第二頁時：

1.先按降序得到前8條數據，而後升序排列着8條數據，

2.這樣第二頁的數據直接跑到了前面，取出4條，

3.而後在倒敘回去就是第二頁的數據

一樣的以此往下類推

當後半數分頁時：

當取最後一頁時：將全部數據升序過來，取出前4條便可

觀察生成的過程

訪問前半數分頁

2016-06-17 08:48:34  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc LIMIT 4

2016-06-17 08:48:43  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 8  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:44  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 12  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:45  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 16  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:45  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 20  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:46  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 24  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:46  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 28  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:47  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 32  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:47  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 36  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:48:48  SELECT * FROM  (  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID desc  LIMIT 40  ) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

訪問後半數分頁

2016-06-17 08:50:51  SELECT * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 4  ) AS T  ORDER BY PostID desc 

2016-06-17 08:51:02  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 5  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:03  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 9  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:03  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 13  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:04  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 17  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:06  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 21  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:07  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 25  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:07  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 29  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:08  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 33  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:09  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 37  ) AS T  ORDER BY PostID desc  LIMIT 4 

2016-06-17 08:51:09  SELECT  * FROM  (  SELECT  *  FROM (SELECT * FROM Post) AS T  ORDER BY PostID ASC  LIMIT 41  ) AS T  ORDER BY PostID desc  LIMIT 4 

來自爲知筆記(Wiz)