有订单和订单_产品表。订单总价应该存储在订单表中，还是根据产品数量和价格计算

Question

So I have the following 3 tables:

Table: Products
Columns: id, name, description, price, currency

Table: Orders
Columns: id, firstName, lastName, phoneNumber

Table: Order_Products
Columns: orderId, productId, quantity

Now I'm trying to figure out where to put the total price of the order and I have 2 ideas:

1. Add a totalPrice column to the Orders table that will contain the sum of the price * quantity of all products in the order, or:
2. Add a price column to the Order_Products table that will contain the the price * quantity of that specific product, and then I'd have to get all Order_Products records for that order and sum their price columns.

I'm not quite sure which option is better, hence why I'm asking for recommendations here.

Answer 1

I would recommend that you store the order total in the orders table.

Why? Basically, order totals are not necessarily the same as the sum of all the prices on the items:

• The prices might change over time.
• The order itself might have discounts.

In addition, the order might have additional charges:

• Discounts applied to the entire order.
• Taxes.
• Delivery charges.

For these reasons, I think it is safer to store financial information on the order when the order is placed.

Answer 2

I woulnd't recommend storing this. This is derived information, that can be computed on the fly whenever needed. If you are going to do the computation often, you can use a view:

create view orders_view as
select o.*, sum(p.price * op.quantity) total_price
from orders o
inner join order_products op on op.orderid = o.id
inner join products p on p.id = op.productid
group by o.id