日期加微秒时间加id后四位生成唯一订单号

function build_order_no($uid){
    //uid后四位
    $uid_len = strlen($uid);
    if ($uid_len != 4){
        if ($uid_len>4){
            $after_uid = substr($uid,-4);
        }else{
            $after_uid = '';
            for ($i = 1 ; $i < (5 - $uid_len) ;$i++){
                $after_uid .= 0;
            }
            $after_uid .= $uid;
        }
    }else{
        $after_uid = $uid;
    }
    //获得微秒数
    $un_number = substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
    return date('ymdhis').$un_number.$after_uid;
}
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