[dba-SQLServer] NULLs

Good Question!

Let's say you have a primary table and a sub table connected by a one to
many relationship.  Normally, the FK in the sub table is equal to the PK in
the main table for at least one record.

But, let say the developer has created a form which is bound only to the sub
table.  In this case, under one condition, that form could add a record to
the sub table with no corresponding record in the primary table.  The
condition is that the table relationship was created so that referential
integrity was NOT enforced.  If referential integrity is enforced, the
database will not allow the creation of a record in a sub table without a
corresponding record in the primary table.

When a developer creates a relationship between two tables in the
Relationships window, a dialog box appears with a checkbox titled 'Enforce
Referential Integrity'.  It's unchecked by default.

Normally, a developer does want referential integrity enforced, but it is
his/her choice.  I've been developing for many years, but can't think of a
time when I did this - but I'm sure someone here can give a good example.

Hope this helps!
Dan

-----Original Message-----
From: dba-sqlserver-bounces at databaseadvisors.com
[mailto:dba-sqlserver-bounces at databaseadvisors.com] On Behalf Of Susan
Harkins
Sent: Monday, March 16, 2009 12:52 PM
To: Discussion concerning MS SQL Server
Subject: Re: [dba-SQLServer] NULLs

I'm more than confused and Gustav, if you can admit it, I can too!

A FK is just a primary key in a related table, so how can it be null to 
begin with? I can see the record not having a match in the related table... 
if that's what you mean.

Susan H.


> Hi Dan
>
> I think you - or someone else? - are contradicting yourself or someone 
> else(?) - at least "me am totalyful confusticated" now!

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