[AccessD] Confused by One to Many versus One to One

On reason for 1-1 is where you have a large number of fields common to all records and a lot 
more that only apply to one type of record.

One possible example would be a vehicle fleet with a mixture of leased and owned vehicles.  
Instead of fields for all the lease details in every vehicle record, you put the lease details in a 
second table with a 1-1 relationship. 



On 3 Jan 2015 at 21:27, John R Bartow wrote:

> I agree with Jim.
> 
> 1-1 relationships can be set up if desired in order to try and be more
> strictly normalized but it rarely makes sense these days and it does
> complicate any UI or queries structures.
> 
> I think I've only ever used one 1-1 table relationship in my own
> developments. I'll have to look and see if I can find out why I did
> that.
> 
> I saw a lot of 1-1 relationships in a very large, government agency,
> database schema in the past but after numerous years of working with
> it there was never an entry in any of those tables.
> 
> -----Original Message-----
> From: accessd-bounces at databaseadvisors.com
> [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Jim Dettman
> Sent: Sunday, November 30, 2014 1:57 PM To: 'Access Developers
> discussion and problem solving' Subject: Re: [AccessD] Confused by One
> to Many versus One to One
> 
> Bill,
> 
>  It's pretty rare to have a 1 to 1.  Pretty much everything will be a
>  1 to M
> or a M to M.
> 
> Jim. 
> 
> -----Original Message-----
> From: accessd-bounces at databaseadvisors.com
> [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Bill Benson
> Sent: Friday, November 28, 2014 07:52 PM To: 'Access Developers
> discussion and problem solving' Subject: [AccessD] Confused by One to
> Many versus One to One
> 
> I almost never make relationships one to one, and yet my databases
> always seem to "work." By work, I mean that I never seem to run into
> situations where I cannot accomplish what I want to, in terms of
> record insertion, queries, etc. So I now have a situation where maybe
> that is not a good idea.
> 
> 
> 
> I have Order and Product tables, one order can contain many products.
> So I required an OrderProducts table to distribute the same OrderID
> across numerous ProductIDs.
> 
> 
> 
> My question is, should the relationship between the Order and
> OrderProduct, on the OrderID and FKOrderID, be 1-to-1, or 1-to-many?
> 
> 
> 
> Likewise, the same question for the OrderProduct and the Product, on
> the ProductID and the FKProductID?
> 
> 
> 
> 
> 
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