redundancy

[john]

Hi all,

I have an invoice to build.
The information come completely from other tables

I am wondering if i should recopy the information
from the other table to my invoice table or simply
put a reference to records in those tables.
Since it is a very important document i feel to
put the information there again, something i don't do
regularly (i prefer to out a reference)
But since the invoice will never change
and hold critical information i am not sure

Any guidelines on that matter?
What is the common use
Regard,

John R.

 

[Jerry Whittle]

One of the rules of normalization is to not store derived or computed data.
However invoices are an exception. With an invoice you need to know what
exactly was sent out. If a price changed and you re-ran the query to get the
invoice, the data would be different.

This is one case where putting the record in an Invoice table makes sense.

Speaking of redundancy, as this data is important, remember to back up your
database to another drive or media frequently.