Preventing data modification in related table

[Johnny777]

Hi

I have a very simple problem but am wracking my brains trying to solve.

I have a table of contacts and a table of invoices linked with a join table

At the moment if you alter some personal details on the contacts ie the surname it will change on the related invoices

Basically I want to prevent this happening

Can anyone kindly point me in the right direction

Many thanks

[efen]

Make the name field in the invoice table a looked up value when the invoice is created