Shopping cart algorithm

Calculate a shopping cart algorithm. after a customer adds a product to the shopping cart for purchase, how can he get the total price of the product? for example, the unit price of Apple is 10 RMB; 5 RMB, 8 RMB for dragon fruit, 3 Apple, 2 bananas, and 5 dragon fruit. Currently, the database is designed like this & nbsp; a table with id and product name, price, put id in Table B (calculate a shopping cart algorithm relative to the id in Table
After the customer adds the product to the shopping cart, how can he get the total price of the product? for example, if the unit price of Apple is 10 yuan, the banana is 5 yuan, the dragon fruit is 8 yuan, and three apples are bought, two bananas and five pitaya. Currently, the database is designed as table a with id, item name, price, and Table B with id (corresponding to table a's id ), how can I get the final price for the number of purchased items (the simplest and most efficient way)? my current method is to first query all the data purchased by this customer in multiple tables, then, use the foreach loop array in php, multiply the price and the number, and add the result to the result. The efficiency is poor.
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