Re: partial "on-delete set null" constraint

> On Sun, 2015-01-25 at 14:09 +0100, Alban Hertroys wrote:
>
> The following link
>
> http://www.databaseanswers.org/codds_rules.htm
>
> sets out Ted Codd's rules according to C.J. Date.

As you might have noticed, those were referred to already upthread, but that is a while ago now.
Although those rules are certainly Codd's, that's an entirely different bit of database theory. It's what I did manage
tofind while searching the Internet for Codd relationality. 

What I understand of them, these 12 rules determine whether a DBMS can be called relational, whereas Codd-relationality
isonly applicable in DBMS's that already qualify as relational and restricts primary keys to non-nullable fields. 

I know it's hard to believe that the Internet does not contain some information, certainly when the information is a
rulethat is applied and documented in pretty much every relational database in existence (but without mentioning it by
nameor why it exists). I'm afraid that might be the case here though. Possibly this could happen because the theory in
questionpredates the internet. 

Alban Hertroys
--
If you can't see the forest for the trees,
cut the trees and you'll find there is no forest.