mysql的order by rand方法实际运用

下文内容主要给大家带来mysql的order by rand方法实际运用，这里所讲到的知识，与书籍略有不同，都是专业技术人员在与用户接触过程中，总结出来的，具有一定的经验分享价值，希望给广大读者带来帮助。

从一次查询中随机返回一条数据，一般使用mysql的order by rand() 方法来实现

例如: 从20万用户中随机抽取1个用户

mysql> select * from user order by rand() limit 1;+-------+------------+----------------------------------+----------+--------------+-----------+| id    | phone      | password                         | salt     | country_code | ip        |+-------+------------+----------------------------------+----------+--------------+-----------+| 15160 | 6549721306 | e4f302120c006880a247b652ad0e42f2 | 40343586 | 86           | 127.0.0.1 |+-------+------------+----------------------------------+----------+--------------+-----------+1 row in set (0.25 sec)mysql> explain select * from user order by rand() limit 1;+----+-------------+-------+------+---------------+------+---------+------+--------+---------------------------------+| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows   | Extra                           |+----+-------------+-------+------+---------------+------+---------+------+--------+---------------------------------+|  1 | SIMPLE      | user  | ALL  | NULL          | NULL | NULL    | NULL | 200303 | Using temporary; Using filesort |+----+-------------+-------+------+---------------+------+---------+------+--------+---------------------------------+1 row in set (0.00 sec)

根据分析结果，运行需要0.25秒，order by rand() 需要使用临时表（Using temporary），需要使用文件排序（Using filesort），效率低下。

改进方法

1.首先获取查询的总记录条数total
2.在总记录条数中随机偏移N条（N=0~total-1)
3.使用limit N,1 获取记录
代码如下：

分析：

mysql> select * from user limit 23541,1;+-------+------------+----------------------------------+----------+--------------+-----------+| id    | phone      | password                         | salt     | country_code | ip        |+-------+------------+----------------------------------+----------+--------------+-----------+| 23542 | 3740507464 | c8bc1890de179538d8a49cc211859a46 | 93863419 | 86           | 127.0.0.1 |+-------+------------+----------------------------------+----------+--------------+-----------+1 row in set (0.01 sec)mysql> explain select * from user limit 23541,1;+----+-------------+-------+------+---------------+------+---------+------+--------+-------+| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows   | Extra |+----+-------------+-------+------+---------------+------+---------+------+--------+-------+|  1 | SIMPLE      | user  | ALL  | NULL          | NULL | NULL    | NULL | 200303 | NULL  |+----+-------------+-------+------+---------------+------+---------+------+--------+-------+1 row in set (0.00 sec)

本篇介绍了mysql order by rand() 效率优化方法 ，更多相关内容请关注。

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