Re: Basic Q on superfluous primary keys

[Greg Smith <gsmith(at)gregsmith(dot)com>]

On Mon, 16 Apr 2007, Merlin Moncure wrote:

> extraordinary cases do happen, like a company overhauling its numbering 
> systems, but such cases can be dealt with by a number of methods 
> including letting RI do its thing.

I think the point Craig was trying to make is that what you refer to here 
as "extraordinary cases" are, in fact, rather common.  I've never seen a 
database built on natural keys that didn't at some point turn ugly when 
some internal or external business need suddenly invalidated the believed 
uniqueness of that key.

The last really bad one I saw was a manufacturing database that used a 
combination of the customer code and the customer's part number as the 
key.  Surely if the customer changes their part number, we should switch 
ours to match so the orders are easy to process, right?  When this got fun 
was when one large customer who released products on a yearly schedule 
decided to change the bill of material for many of their parts for the new 
year, but re-used the same part number; oh, and they were still ordering 
the old parts as well.  Hilarity ensued.

> it is especially unclear how adding an integer to a table will somehow 
> magically solve these problems.

If the key is a integer, it's always possible to figure out a trivial map 
that renumbers the entire database programmatically in order to merge two 
sets of data.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD