PHP生成唯一订单号

<?php
     $yCode = array('A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J');
     $orderSn = $yCode[intval(date('Y')) - 2011] . strtoupper(dechex(date('m'))) . date('d') . substr(time(), -5) . substr(microtime()] 2, 5) . sprintf('%02d', rand(0, 99));
?>

A422694333616096

<?php
    function build_order_no(){
        return date('Ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
    }
    echo build_order_no();
?>

2014062356100485
2014062349535399