随机查询一行记录的实现(替代mysql的rand())

// 千万不要这样做：
$r= mysql_query("SELECT username FROM user ORDER BY RAND() LIMIT 1");
 
// 这要会更好：
$r= mysql_query("SELECT count(*) FROM user");
$d= mysql_fetch_row($r);
$rand= mt_rand(0,$d[0] - 1);
 
$r= mysql_query("SELECT username FROM user LIMIT $rand, 1");