database design for sale system - mysql

Question

In a simple sales sample I have 3 primary tables: Order, Product, Orders_Products:
Product table
+----+-----------+
| id | name |
+----+-----------+
| 1 | A |
| 2 | B |
+----+-----------+
order table
+----+---------+------------+------------+---------------------+
| id | user_id | total_cost | order_date | status_id |
+----+---------+------------+------------+---------------------+
| 1 | 5 | 25.00 | 2012-02-03 23:30:24 | 1 |
| 2 | 7 | 30.00 | 2012-02-13 18:06:12 | 1 |
+----+---------+------------+------------+---------------------+
orders_products table
+----+----------+------------+--------+
| id | order_id | product_id | cost |
+----+----------+------------+--------+
| 1 | 1 | 34 | 10.00 |
| 2 | 1 | 25 | 10.00 |
| 3 | 1 | 27 | 2.50 |
| 4 | 1 | 36 | 2.50 |
| 5 | 2 | 75 | 25.00 |
| 6 | 2 | 74 | 5.00 |
+----+----------+------------+--------+
But in my system:
A user adds money into his account then he can spend it
Products are services like Product A: user can post 5 Ads so when user post a Ads that 5 become 4 and so on.
How should I design DB for it??

Answer 1

You currently have no table to store customer data. I would strongly advise creating one using an Auto-Increment ID field, a name field and a field to store the money on their account which can be modified when the add money to it or purchase something.
In the Order table, the user_id field should be a foreign key from the Customer table I just told you how to create.
If you want to better understand what you should be doing, I would recommend looking at the Entity-Relationship Model
I don't entirely understand what your second question is, can you explain it in more detail? Are all the products just a set number of ads that the customer can post?