如何从日期和插入数据库生成唯一的订单号？

$order = new Order();
$dt = new DateTime;           
$order->restaurant_id = 1;          
$order->order_no = $dt->format('Y'.'m'.'d'.'0000'); 

'How Make unique order id from date and 0000 number Auto Increment'

Your $order->id should be unique already. I suggest using $order->order_no = $d->format('Ymd').$order->id without involving restaurant_id that way you will easily know the the part after first 8 characters (YYYYmmdd) is the order id to find from database.