摘要：
一直以为MySQL随机查询几条数据，就用SELECT * FROM 'table' ORDER BY RAND() LIMIT 5就可以了。但是真正测试一下才发现这样效率非常低。一个15 万余条的库，查询5条数据，居然要8秒以上 查看官方手册，也说rand()放在ORDER BY 子句中会被执行多次，自然效率及很低。 You cannot use a column with RAND() values in an ORDER BY clause, because ORDER BY would evaluate the column multiple times. 搜索Googl 阅读全文
