隨機獲取數據庫的數據

 

最近的在開發自己的博客，里面有個功能需要隨機推薦這個功能。

 

不同數據庫隨機獲取 10 條數據

轉載：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([一個自動編號字段])

這條語句在 Access 中的“查詢”中是可以運行並得到隨機結果的，但在 ASP.NET等后台程序代碼中卻無法得到預期的隨機效果。
正確的寫法如下：

以ASP.NET為例：

Random random = new Random(System.Guid.NewGuid().GetHashCode());
int r = random.Next();
string sql = "SELECT TOP 10 * FROM T_USER ORDER BY RND(" + (-r) + "*自動編號字段)"

 

 

Mysql數據庫

轉載：http://www.111cn.net/database/mysql/40168.htm

普通方法

本人現在使用的是Mysql數據庫。

這條sql語句適用於數據庫數據量小時的方式（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;

 

再把語句完善一下，加上MIN(id)的判斷。

完整查詢語句是：

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;