Re: Oracle NULL vs '' revisited

> Loosely quoted, you stated "ISO country codes are not keys, as
> they change".

Loosely? Made up more like.

I said and I quote properly...

<START QUOTE>
"These are some examples of a natural key that have changed in the past 10 years ...

ISBN number

ISO country code
"
<END QUOTE>

And you added this "are not keys, as they change"

People tell us to use industry standard codes for natural keys - aka country, isbn etc... these have changed, unless you used a surrogate or artifical key of your own then you had to change the data.

Consider a book 'The XYZ of blah', pre ISBN change it might of been x123456 and post change it is now both x123456 and z654321 - the single title "The XYZ of blah" has two natural keys (two uniquely identifyable, verifyable keys).

DA stated this

<START QUOTE>
Natural keys can not change. If it can change IT IS NOT A KEY it is just a value.
<END QUOTE>

The Natural key to a book is it's ISBN number, that has changed over the past 10 years.

The only thing I can interprit from this is that you guys create your own artifical key probably based on a auto incrementing number or do you like the rest of use correctly use ISBN as the natural key but create a surrogate as well and use the surrogate for table and application plumbing (foreign keys, internal values passed between the app and the db - eg. the VALUE property of the <SELECT> HTML tag.

-- 
Tony Rogerson, SQL Server MVP
http://sqlblogcasts.com/blogs/tonyrogerson
[Ramblings from the field from a SQL consultant]
http://sqlserverfaq.com
[UK SQL User Community]