做项目中遇到所有的常用知识点（javascript、php、mysql、apache、nginx）更新

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