每日订单号从0001开始

        $a=85;//从数据库查询今日订单总条数
$a=$a+1;
$time = date('Ymd',time());
if($a > 0){
$order ="000".$a;
}else if($a > 9){
$order ="00".$a;
}else if($a > 99){
$order ="0".$a;
}else if($a > 999){
$order =$a;
}

$num = "B".$time.$order;
var_dump($num);