[AccessD] Access and SQL Server

Doesn't SQL server require a field with a unique index in order for the table to be updatable?

AuthorID cannot be unique (obviously)
BookID might not be unique (as some books have multiple authors)

So don't you need LinkID - Autonumber PK?

Lambert

-----Original Message-----
From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Jim Dettman
Sent: Tuesday, March 01, 2011 1:40 PM
To: 'Access Developers discussion and problem solving'
Subject: Re: [AccessD] Access and SQL Server


 So on a many to many linking table you would do this:

tblBooksAndAuthors
LinkID - Autonumber - PK
AuthorID - Long - FK to tblAuthors - CK-A BookID - Long - FK to tblBooks - CK-B

And not simply:

tblBooksAndAuthors
AuthorID - Long - FK to tblAuthors - PK-A BookID - Long - FK to tblBooks - PK-B

 and eliminate an index?  If so, why not?

Jim.
 

-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com] On Behalf Of jwcolby
Sent: Tuesday, March 01, 2011 12:47 PM
To: Access Developers discussion and problem solving
Subject: Re: [AccessD] Access and SQL Server

When I create a table in any datastore, the first thing I do is create an autoincrement PK.  I no longer even think about it - if need a table, I need an autonumber pk!

I then proceed to create the fields.

John W. Colby
www.ColbyConsulting.com

On 3/1/2011 12:17 PM, Jim Lawrence wrote:
> Many years ago I was taking over an Access project as the clients were 
> having problems with their invoices. After about two days I discovered 
> the problem with the invoice.
>
> It appears that the subform was connected to the main form by grouping 
> together 3 fields, creating natural foreign key between the two 
> tables. By some odd set of bad luck certain combinations of this key 
> hash matched another unrelated key value and the sub form data was 
> pulling from
multiple
> invoice details.
>
> The only reliable solution was to move all the tables to auto PKs but 
> it cost the client a fair chunk of change. For that reason I have 
> never inflicted natural keys, on a client, no matter how strong the temptation.
>
> Jim
>
>
>
> -----Original Message-----
> From: accessd-bounces at databaseadvisors.com
> [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Stuart
McLachlan
> Sent: Monday, February 28, 2011 3:00 PM
> To: Access Developers discussion and problem solving
> Subject: Re: [AccessD] Access and SQL Server
>
> I see a lot of sense in it having a separate Autonumber PK.   This is a
> classic case of why
> you should not use a natural key as your PK.
>
> What happens when the Description changes and the existing Code is no
longer
> an accurate
> short representation of Description?  Do you change it throughout all 
> the tables which store it or do you leave your customer with strange 
> Codes which don't match the description
>
> (And please don't tell me that you use Relationships with "Cascade Update"
> turned on.)
>
>
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