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1.Mysql随机取数据，性能最好的方法：
用join取出一条
SELECT * FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * (SELECT MAX(id) FROM `table`)) AS id) AS t2 WHERE t1.id >= t2.id ORDER BY t1.id ASC LIMIT 5;
取出多条（最大值-最小值）* 随机数 +最小值
SELECT * FROM users WHERE userId >= ((SELECT MAX(userId) FROM users)-(SELECT MIN(userId) FROM users)) * RAND() + (SELECT MIN(userId) FROM users) LIMIT 1
做项目中遇到所有的常用知识点（javascript、php、mysql、apache、nginx）更新
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原文地址：http://www.cnblogs.com/bc8web/p/5904489.html
