Oracle row_number() 高效分页-MySQL-Tutorial-php.cn

Oracle row_number() 高效分页

WBOY

Freigeben： 2016-06-07 17:45:59

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利用自带的函数分页当然会高效一些了，本文章介绍一篇关于Oracle row_number() 高效分页方法，有需要的朋友参考一下。

第一步：我先用rownum

代码如下

复制代码

-- row_number，不是rownum
--根据n_count从大到小排列，每页3条
SELECT ROWNUM r,t.* FROM t_news t
WHERE ROWNUM ORDER BY t.n_count DESC
--问题：为什么order by以后，行号是乱的？
SELECT ROWNUM r,t.* FROM t_news t
--原因：先分配了行号，再根据n_count排序

--所以必须排序，再生成行号
SELECT ROWNUM r,t.* FROM (
SELECT t.* FROM t_news t ORDER BY t.n_count DESC ) t

--分页
--err
SELECT ROWNUM r,t.* FROM (
SELECT t.* FROM t_news t ORDER BY t.n_count DESC ) t
WHERE r between 1 AND 3

--第1页
SELECT ROWNUM r,t.* FROM (
SELECT t.* FROM t_news t ORDER BY t.n_count DESC ) t
WHERE ROWNUM between 1 AND 3

--第2页
SELECT ROWNUM r,t.* FROM (
SELECT t.* FROM t_news t ORDER BY t.n_count DESC ) t
WHERE ROWNUM between 4 AND 6
--error: ROWNUM必须从1开始！
SELECT k.* FROM (
SELECT ROWNUM r,t.* FROM (
SELECT t.* FROM t_news t ORDER BY t.n_count DESC ) t
) k
WHERE r BETWEEN 4 AND 6

--麻烦，效率低！

*****第二步:我用row_number() over()函数

代码如下

复制代码

t2.* from
(select t.*,row_number()over(order by t.n_count desc) orderNumber from t_news t order by t.n_count desc)t2 where orderNumber between 1and 3;

*****************************************************************************************************************************************88
SELECT * FROM (
SELECT t.*,row_number() over(ORDER BY n_count DESC) r
FROM t_news t
ORDER BY t.n_count DESC
) t
WHERE r BETWEEN 4 AND 6

--通用语法：解析函数() over(partition by 字段 order by 字段)