I know setting up a foreign key between a two tables with master detail
relationship is a good practice. I wonder if I have a lookup
relationship is it good to set up a foreign key. An example of lookup
relationship is ...

a product table and a invoice_details table. When inserting a record in
invoice_details, a list of product(less than 50 items) from the product
table are available choices. I don't know if there's a need for setting
up a foreign for this one, but my reason is to prevent a record from
product table to be deleted when there is a record in invoice_details.

Please advice.


regards,
james