数据库设计建议

Question

I am building a shopping cart system on my localserver for practice.

Now, I am using sessions to insert the product to the MySQL database, but I am creating a table for each of the sessions. I know this is not an ideal way to do things.

My question:

Should I define a number of rows in the sessions table, so that there will be a maximum number of items added to the cart?

So if I re design the table it would be

User INT NULL,
product_1 INT NULL,
product_2 INT NULL,
...
....

I know that creating a table for each of the orders will only cause problems in the future

Answer 1

No, this design will be incredibly difficult to maintain. Instead, have one table that will hold all cart data; something like:

User    Product    Quantity
2       5          1
2       3          3
2       7          1
3       5          2
3       6          2

where the "user" column is a foreign key on the user table (or cart table, whichever), and the "product" column is a foreign key on the product table. That way there is no restriction on the number of unique products in the cart at one time.

Answer 2

It would probably be better to check number of items in cart before adding a new item to the database. If number of cart items is equal to the maximum, then don't allow another item to be added or row to be added to database. I don't think it is possible to set a maximum number of rows in an SQL table and if it is possible, it probably isn't good practice.

Why not have a single table which holds all cart items (for all users) and store a unique customer ID in the Session variable which references to a row in the SQL cart table.

Something like this...

Columns: CustomerID | ProductID | QTY

Row 1: 1293993933 | 393939399 | 3
Row 2: 1293993933 | 339933992 | 4

Store the customer ID in a session variable ($_SESSION['CustomerID'] if you're using PHP)

Do a select count SQL query each time a product is added to cart. If it equals maximum allowed cart items, don't allow user to run the insert into SQL command.

Hope this helps