[Info-ingres] Nonidentifying/optional relationship with NULL FK?

[Martin Bowes]

Hi Nikos

Yes I have heaps of these sorts of cases.

Typically a column has a default value (often zero) which is not put into the referenced table as a key value as the owner point blank refuses to allow this.

Ergo I can't use a FK constraint and have to enforce the constraint using a rules fired procedure (RFP) instead. It's a bit tedious to write all these RFPs so if anyone in Ingres Techy land would like to give me a Christmas pressie...

Marty

-----Original Message-----
From: nikosv [mailto:nikos.vaggalis at gmail.com] 
Sent: 21 December 2018 08:18
To: info-ingres at lists.planetingres.org
Subject: [Info-ingres] Nonidentifying/optional relationship with NULL FK?

Searching for "non-identifying relationship where the FK can be null" I stumbled upon the "Nonidentifying/optional" part on page 279 of the book "Beginning Relational Data Modeling"

https://books.google.com/books?id=62CFtFea0NsC&pg=PA279&lpg=PA279&dq=nullable+foreign+key+optionality&source=bl&ots=CM0t0Jfb6L&sig=9F_WdkXta3v-3Uo6Ym8r7UsYJ9A&hl=en&sa=X&ved=0ahUKEwi1v_Sm77rTAhUJOsAKHXM_BMgQ6AEISjAG#v=onepage&q=nullable%20foreign%20key%20optionality&f=false

Is that a valid point? Is it something you came across or have used it? 
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