Question

im new to database design and im trying to create an ERD for a pharmacy that sells products online and also accepts repeat prescriptions orders to customers.

Here is the link to my ERD:
https://i.stack.imgur.com/vmeOD.png

I’m wondering how i could only make use of only one ‘payment’ and ‘card details’ entity for both orders, so have i have 2 entities for each order. Would i be able to make a relationship between the ORDER TYPE entity and payment/card details entity.

Any help would be appreciated. thanks

Answer 1

I’m trying to find a good reason forh aving both Prescription_Order and Product_Order. There should just be an Orders (pluralized because ORDER is a reserved word everywhere) table, where the Customer_Recurring_Order table (with a natural key of references to Customer and Product) breaks out the rules for a customer’s recurring orders, regardless of whether they are prescription in nature or not. Your medicine attribute properly belongs as a record in the product table.

Also, the Card Details table should properly be linked to one or more Customer, as I’m pretty sure that card details are functionally dependent on the existence of a customer.

Once you’ve cleaned those up, you only need one Payment or Card Details entity. A good design principle to remember is that if two entities have all the same attributes, they probably aren’t two different entities.

Why didn’t you break out shipping information into a separate entity, Order_Shipment. Will all shipments always contain all portions of a customer’s order?