从数据库随机取出数据

SELECT description FROM question ORDER BY RAND() LIMIT 1;

在ORDER BY从句里面不能使用RAND()函数，因为这样会导致数据列被多次扫描。

SELECT description FROM question WHERE id >= (SELECT FLOOR(RAND() * (SELECT MAX(id) FROM question))) ORDER BY id LIMIT 1;

SELECT description FROM question AS t1 JOIN (SELECT ROUND(RAND() * (SELECT MAX(id) FROM question)) AS id) AS t2 WHERE t1.id >= t2.id ORDER BY t1.id ASC LIMIT 1;