1，测试表结构：
mysql> desc test_user;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(50) | NO | | NULL | |
| age | int(11) | YES | | NULL | |
| address | varchar(50) | YES | | NULL | |
2，添加随机字段和索引：
mysql> alter table test_user add random double;
mysql> alter table test_user add index (random)
3，填充随机字段数据:
mysql> update test_user set random = rand();
4,随机返回一条数据：
mysql> select id ,name from test_user where random > rand() order by random limit 1;
+----+------+
| id | name |
+----+------+
| 9 | com |
+----+------+
1 row in set (0.00 sec)
mysql> select id ,name from test_user where random > rand() order by random limi
t 1;
+----+------+
| id | name |
+----+------+
| 7 | www |
+----+------+
1 row in set (0.00 sec)
