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【思路】-分页-双top分页算法的原理
描述：实现分页的一种算法
大致过程：访客访问不同的分页，为这个当前页生成动态的查询SQL，然后送到数据库中执行
输入：总条数，每页多少条，第几页，查询的SQL，排序的字段
注意：传入的排序字段需要构成唯一记录，这就意味着不能单独的使用SortOrder这个单独排序
字段反转：SortOrder asc,PostID desc；反转之后是SortOrder desc,PostID asc；
实现过程
访问第一页
访问最后一页
访问前半数分页
访问后半数分页
100条数据 每页显示4条 按照ID降序 排序
当取第一页时：直接对所有数据降序取出前4条
当取第二页时：
1.先按降序获得前8条数据，然后升序排列着8条数据，
2.这样第二页的数据直接跑到了前面，取出4条，
3.然后在倒叙回去就是第二页的数据
同样的以此往下类推
当后半数分页时：
当取最后一页时：将所有数据升序过来，取出前4条即可
观察生成的过程
访问前半数分页
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
访问后半数分页
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
来自为知笔记(Wiz)
【思路】-分页-双top分页算法的原理
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