摘要:
static int GetRandomSeed( ){byte[] bytes = new byte[4];System.Security.Cryptography.RNGCryptoServiceProvider rng = new System.Security.Cryptography.RN... 阅读全文
摘要:
转载请说明。R语言官网:http://www.r-project.org/R语言软件下载:http://ftp.ctex.org/mirrors/CRAN/ 注:下载时点击 install R for the first time下面进行一个简单的入门程序学习。先新建一个txt,叫做 Ric... 阅读全文
摘要:
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;但是这样会产生连续的5条记录。解决办法只能是每次查询一条,查询5次。即便如此也值得,因为15万条的表,查询只需要0.01秒不到。 阅读全文