Re: Unique Keys
Date: Thu, 25 Nov 2004 11:33:36 -0500
Message-ID: <04eh72-nan.ln1_at_pluto.downsfam.net>
Tony Andrews wrote:
>> Tony Andrews wrote: >> > Mikito has given an answer that works, but as you say does not use
> a
>> > unique constraint (how could it?) But I think you are looking at
> this
>> > the wrong way round: a unique constraint isn't primitive, it is a >> > shorthand for a constraint that could be more generally expressed
> as:
>> >> This is an interesting paragraph. I would not have said, "unique is >> shorthand", but it does actually express the idea, a declarative
> constraint
>> invokes a lot of procedural code inside of the server tha we never
> see, we
>> just see the effects. But anyway, unique constraints are
> declarative, and
>> Mikito's is not, Mikito's stands as a *special* *case* that requires
> a
>> programmer to code up some SQL instead of simply specifying the
> unique
>> constraint in pure scalars.
>
> This is where you and I fundamentally disagree. As far as I am
> concerned, Mikito's constraint IS declarative. It declares a condition
> that must always be true, and does NOT specify in procedural code how
> that constraint should be enforced. It defines "what" not "how" in
> other words. Your personal definition of declarative seems to mean
> "requires no knowledge of syntax". That may be a laudable aim, but it
> is not what "declarative" normally means:
>
> http://en.wikipedia.org/wiki/Declarative_programming
My footnote said that I was using the word "declarative" in the sense it is most often used in this NG, which is simple propositions. Simple propositions are the equivalent of scalar data, which is how I specify my databases (and how I specify my scheduling table as well). But to avoid confusion, I will avoid the term.
But I believe my original paragraph still said it, that ad-hoc SQL does not constitute a scalar specification of data. It is a one-time bit of code that accomplishes a single goal and provides no more useful information. Every interaction with that table will require more ad-hoc code. It requires ad-hoc documentation.
>
>> The answer I came up with, and that I am using, allows me to
> declaratively
>> specify[1] the start/end combination as being a unique primary key,
> and
>> more importantly, to define foreign keys into it that do not require
> the
>> "run out". Because I use a code generator, this will generate code
> that is
>> superficially close to Mikito's, but different in many respects (most >> importantly that no programmer has to write it). Probably >> the most crucial respect is the ability to present a foreign key that
> can
>> be used without introducing ad-hoc code in every query.
> Are you going to tell us how you do it? I still don't get it.
Yes, but I wanted to see if anybody else had any treatments to provide. Actually I was just wondering if anybody else considers it possible, as I said in my original post.
-- Kenneth Downs <?php $sig_block="Variable scope? What's that?";?>Received on Thu Nov 25 2004 - 17:33:36 CET