Shopping cart schema with multiple product tables I have a shopping cart table used to store customer id and product id of their chosen items. However I have multiple product tables, for example cars, books, houses. I started out with one table but then realized using an auto increment key for the product tables might cause a problem, as I will not know which table to join the shopping cart with. I originally started out with one table so I did not have this problem before, but now I have to expand it to accommodate two additional product tables. I am looking for some help in how to restructure this schema to properly store products to the cart table.

Cars

╔══════════╦═══════════╦══════════╗
║ CarID    ║ Model     ║ Brand    ║
╠══════════╬═══════════╬══════════╣
║        0 ║ E 320     ║ Bmw      ║
║        1 ║ JR 505    ║ Audi     ║
╚══════════╩═══════════╩══════════╝


Books

╔══════════╦═══════════╦══════════╗
║ Book ID  ║ Author    ║ Title    ║
╠══════════╬═══════════╬══════════╣
║        0 ║ A.R       ║ Smithy   ║
║        1 ║ J.R.      ║ Hailey's ║
╚══════════╩═══════════╩══════════╝


Houses

╔══════════╦═══════════╦══════════╗
║ HouseID  ║ Address   ║ Town     ║
╠══════════╬═══════════╬══════════╣
║        0 ║ Belmont Av║ Bull Bay ║
║        1 ║ Cedar Drv ║ Cinclairs║
╚══════════╩═══════════╩══════════╝


Cart Table

╔══════════╦═══════════╦══════════╗
║ CartID   ║ memberID  ║ ProductID║
╠══════════╬═══════════╬══════════╣
║        0 ║ 3         ║ 1        ║
║        1 ║ 5         ║ 0        ║
╚══════════╩═══════════╩══════════╝
I would solve this by adding a generic PRODUCT table containing the attributes which are common for all products (including the ProductID) and a ProductType column describing the type of product (Car, Book etc). Tables CAR, BOOK can then contain the same ProductID as in the main PRODUCT table and attributes which are specific to their product type.