Re: Calculated/derived fields

lgoodbar@xxxxxxxxxxxxxx wrote:

No real issues with what you propose. One thing database purists go on
about is "do not store calculated fields in a table". Just as you
describe, keeping itdlr7 correct can be difficult.

Just the phrase "database purist" makes me itch <grin>.

Seriously, though, there are valid cases for storing derived fields. We called this "strategic denormalization" back in the day. A perfect example is storing the total amount for an order. Yes, you can calculate it every time by adding the total amount of every line and the total tax and total freight, but in an order with hundreds of line items, that's not exactly a good thing, especially since it's a value that displayed often and even sorted on.

Not quite the issue here - this is a point-in-time calculation like the BPCS onhand inventory. However, you have to ask yourself how many times a given price will be read vs. the number of time the price is changed. The only rule in database design is that all rules depend on the business requirement.

Joe