数据表里有90万条数据，需要随机取10条...怎样才能执行时间短？
用 $RandomList = M('videos')->limit(10)->order('rand()')->select();
执行时间：Process: 416.4988s ( Load:0.0060s Init:0.0230s Exec:416.4038s Template:0.0660s ) | DB :3 queries 0 writes | Cache :0 gets 2 writes | UseMem:2,317 kb | LoadFile:37 | CallFun:71,1410