插入数据

nsert into downitems (chid,catid,softid,....) 
SELECT chid,catid,softid... FROM `downitems` WHERE itemid >= (SELECT floor(RAND() * (SELECT MAX(itemid) FROM `downitems`))) ORDER BY itemid LIMIT 1000; 

原文：http://my.oschina.net/u/2484242/blog/528693