php 自动生成订单编号二种方法

<?php
$dingdanhao = date("Y-m-dH-i-s");
$dingdanhao = str_replace("-","",$dingdanhao);
$dingdanhao .= rand(1000,999999);

print $dingdanhao;
?>

<?php
$ddnumber=substr(date("ymdHis"),2,8).mt_rand(100000,999999);
echo $ddnumber;
?>