随机获取数据库的数据

今天药忘吃喽~ 2021-12-15 02:17 225阅读 0赞

# 随机获取数据库的数据 #

**最近的在开发自己的博客，里面有个功能需要随机推荐这个功能。**

# **不同数据库随机获取 10 条数据** #

**转载：[https://www.cnblogs.com/gc2013/p/3580796.html][https_www.cnblogs.com_gc2013_p_3580796.html]**

SQL Server:
    SELECT TOP 10 * FROM T_USER ORDER BY NEWID()
    
    ORACLE:
    SELECT * FROM (SELECT * FROM T_USER ORDER BY DBMS_RANDOM.RANDOM()) WHERE RONUM <= 10
    
    MySQL:
    SELECT * FROM T_USER  ORDER BY  RAND() LIMIT 10
    
    Access:
    SELECT TOP 10 * FROM T_USER ORDER BY rnd([一个自动编号字段])
    
    这条语句在 Access 中的“查询”中是可以运行并得到随机结果的，但在 ASP.NET等后台程序代码中却无法得到预期的随机效果。
    正确的写法如下：
    
    以ASP.NET为例：
    
    Random random = new Random(System.Guid.NewGuid().GetHashCode());
    int r = random.Next();
    string sql = "SELECT TOP 10 * FROM T_USER ORDER BY RND(" + (-r) + "*自动编号字段)"

# Mysql数据库 #

转载：[http://www.111cn.net/database/mysql/40168.htm][http_www.111cn.net_database_mysql_40168.htm]

## 普通方法 ##

本人现在使用的是Mysql数据库。

这条sql语句适用于数据库数据量小时的方式（普通方式，效率低下）：

SELECT * FROM T_USER  ORDER BY  RAND() LIMIT 10

## JOIN的方法 ##

SELECT * 
    
    FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM `table`) – (SELECT MIN(id) FROM `table`)) + (SELECT MIN(id) FROM `table`)) AS id) AS t2 
    
    WHERE t1.id >= t2.id 
    
    ORDER BY t1.id LIMIT 10;

再把语句完善一下，加上MIN(id)的判断。

完整查询语句是：

SELECT * FROM `table`
    
    WHERE id >= (SELECT floor( RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`)) + (SELECT MIN(id) FROM `table`)))
    
    ORDER BY id LIMIT 1;
    
    SELECT *
    
    FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`))+(SELECT MIN(id) FROM `table`)) AS id) AS t2
    
    WHERE t1.id >= t2.id
    
    ORDER BY t1.id LIMIT 1;

转载于:https://www.cnblogs.com/-wenli/p/10485111.html

[https_www.cnblogs.com_gc2013_p_3580796.html]: https://www.cnblogs.com/gc2013/p/3580796.html
[http_www.111cn.net_database_mysql_40168.htm]: http://www.111cn.net/database/mysql/40168.htm