MySQL随机查询出一条记录

$sql = “SELECT * FROM pinglun WHERE id >= ((SELECT MAX(id) FROM pinglun)-(SELECT MIN(id) FROM pinglun)) * RAND() + (SELECT MIN(id) FROM pinglun) LIMIT 1″;

这样写效率比较高，，千万不要用order by rand（）那种，，数据量大了，order一下效率很低