Question

Here is the situation:

I got a database which record the relationship between CUSTOMER and ORDER, INVOICE, PAYMENT etc.

My current design is: CUSTOMER links to ORDER, ORDER links to INVOICE, and INVOICE links to PAYMENT.

My question is, I actually want to know which CUSTOMER is dealing with the ORDER, the INVOICE and the PAYMENT. So do I have to put the CUSTOMER_ID in every table which I want to show the CUSTOMER in as a FK? Will it

Or I can just present it by query?

Answer 1

No, you don’t. You should just write a query with multiple joins, if you aim to follow proper database design and avoid redundant data storage.

E.g.:

SELECT c.CUSTOMER_ID, ..., p.PAYMENT_ID, ...
FROM CUSTOMER c,ORDER o,INVOICE i,PAYMENT p
WHERE c.CUSTOMER_ID = o.CUSTOMER_ID
and o.ORDER_ID = i.ORDER_ID
and i.INVOICE_ID = p.INVOICE_ID