Question

I don’t know a good way to maintain sums depending on dates in a SQL database.

Take a database with two tables:

Client

• clientID
• name
• overdueAmount

Invoice

• clientID
• invoiceID
• amount
• dueDate
• paymentDate

I need to propose a list of the clients and order it by overdue amount (sum of not paid past invoices of the client). On big database it isn’t possible to calculate it in real time.

The problem is the maintenance of an overdue amount field on the client. The amount of this field can change at midnight from one day to the other even if nothing changed on the invoices of the client.

This sum changes if the invoice is paid, a new invoice is created and due date is past, a due date is now past and wasn’t yesterday…

The only solution I found is to recalculate every night this field on every client by summing the invoices respecting the conditions. But it’s not efficient on very big databases.

I think it’s a common problem and I would like to know if a best practice exists?

Answer 1

You should read about data warehousing. It will help you to solve this problem. It looks similar as what you just said

“The only solution I found is to recalculate every night this field
on every client by summing the invoices respecting the conditions. But
it’s not efficient on very big databases.”

But it has something more than that. When you read it, try to forget about normalization. Its main intention is for ‘show’ data, not ‘manage’ data. So, you would feel weird at beginning but if you understand ‘why we need data warehousing’, it will be very very interesting.

This is a book that can be a good start http://www.amazon.com/Data-Warehouse-Toolkit-Complete-Dimensional/dp/0471200247 , classic one.