Hey Rick,
A "constraint" does just what it says - it enforces a rule.
A "foreign-key constraint" refers to a type of constraint that, when
placed on a column in one table, makes sure any values in that column
reference a value in a column in a second ("foreign") table.
Basically, if I had the following:
User
---------
UserId
FavoriteColorId
Color
----------
ColorId
I could place a "foreign-key constraint" on User.FavoriteColorId that
referred to Color.ColorId to make sure no values were ever entered
into User.FavoriteColorId that weren't in Color.
-Joe
On Tue, 29 Mar 2005 23:48:45 -0500, Rick Faircloth
<[EMAIL PROTECTED]> wrote:
> > I am of course, assuming that you know the difference between a
> > foreign-key constraint (which ensures data integrity by producing an
> > error if an insert/update/delete statement would create a conflicting
> > state in the data - in other words it doesn't allow the database to
> > ignore errors in your code), and simply having two tables which are
> > joined in your ad-hoc queries.
>
> Sorry, that's what I'm saying I don't understand. I realize you probably
> don't want to go too much into the detail I'd need to full understand, but
> if you have a good reference online for that I'd study it for clarification.
> I've never used foreign-key constraints...sounds like something I should
> learn and implement in my coding...
>
> It sounds like something I do when I don't allow the deletion of a
> Real Estate agent when they still have properties in the database
> assigned to them, which would ...anything to do with something like that?
>
> Rick
>
>
> -----Original Message-----
> From: S.Isaac Dealey [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, March 29, 2005 10:49 PM
> To: CF-Talk
> Subject: RE: Database Model Suggestions - Elections
>
> > Hmmm....I took a look at that page and was pleased to see
> > that I follow the standards closely, but I've never used a
> > "corresponding constraint name"...
>
> > I've always used what I considered foreign keys, by using
> > the Primary Key of one table in another as a linking
> > field, like the Customer_ID in the Order table...but what's
> > the purpose of a "corresponding constraint name" and the
> > FKn...etc., as described below?
>
> > Rick
>
> > The corresponding constraint names should be the table
> > name followed by _FKn
> > where n = 0..9 (e.g., ADDRESS_FK1, ADDRESS_FK2)
>
> Typically you would want the naming convention applied to the foreign
> key constraints if you're in the habbit (or environment) of creating
> and dropping them using hand-crafted SQL scripts. I used to work for a
> company in Orlando where this was the case several years ago (just
> before the dot-com collapse), although unfortunately most of the
> companies I've worked for have taken an alternate route and simply
> decided that foreign-key constraints are not to be used (BLECH!). I
> use foreign-key constraints consistently in my own work but always
> handle them in an automated fashion, so I never have any real need for
> a naming convention, since I'm not hand-coding the create or drop
> statements generally speaking.
>
> I am of course, assuming that you know the difference between a
> foreign-key constraint (which ensures data integrity by producing an
> error if an insert/update/delete statement would create a conflicting
> state in the data - in other words it doesn't allow the database to
> ignore errors in your code), and simply having two tables which are
> joined in your ad-hoc queries. The former is what I use - the latter
> is what I'm forced to work with at my day-job.
>
> s. isaac dealey 954.522.6080
> new epoch : isn't it time for a change?
>
> add features without fixtures with
> the onTap open source framework
>
> http://macromedia.breezecentral.com/p49777853/
> http://www.sys-con.com/author/?id=4806
> http://www.fusiontap.com
>
>
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