I am developing web site to compare coupons.
we will have all information from yahoo, ecoupon.com and couponshopping.com.
The following tables shows the Denny's coupon avaiable from three sites
from ecoupon.com you have Free Drink, yahoo 2 for 1, and couponshopping 10%
accordingly.

Shop Master Table
| shop_id | ecoupon_id | yahoo_id | couponshopping_id | shop_name |
shop_address
| 1 | ec00001 | yh00001 | cs00001 |
Denny's | 1233 Georgia Ave.

Coupon Master Table
| id | coupon_id | coupon_content |
| 1 | ec00001 | Free Drink |
| 2 | yh00001 | 2 For 1 |
| 3 | cs00001 | 10% OFF |

The problem I am facing now is that what if I add another site handle
coupons say EbayCoupon.com
but uses similar id like ec00001. How can I optimize this table so that the
data won't be duplicated and normalized for the best performance but still
be able to compare the coupons from multiple web sites.

Thanks in advance.

MD