Re: A tale of duplicates
Date: Sat, 09 Oct 2004 08:42:06 -0400
Message-ID: <vam8kc.q5v.ln_at_mercury.downsfam.net>
Laconic2 wrote:
> This thread is derived from the other thread about "true relational".
> Here's what Kenneth said in that thread:
>
> "Kenneth Downs" <firstinit.lastname_at_lastnameplusfam.net> wrote in message
> news:hqd6kc.4go.ln_at_mercury.downsfam.net...
>> It said often here that no commercially available DBMS is truly
> relational,
>> but I haven't seen a succinct list of reasons. What are they? >> >> One that I have gleaned from lurking is that the DBMS's allow duplicates,
> as
>> in:
>>
>> CREATE TABLE AnyTable (col1 char(1), col2 char(1), col3 char(1));
>> INSERT INTO AnyTable (col1,col2,col3) VALUES ('A','B','C');
>> INSERT INTO AnyTable (col1,col2,col3) VALUES ('A','B','C');
>>
>> The table create specifies no constraints, and so the next two insert
>> statements are both allowed. The objection to this seems to be that the
>> RDM requires an implied unique constraint on all columns of all tables.
>> Because such a constraint is not present, they are not truly relational.
>>
>> Is that right?
>
> I was once interviewing with a customer, and when the asked me to descibe
> my
> skills, I happened to mention data normalization. "What's normalization?"
> they asked. I tried to give a straight answer, but I could tell from
> their
> facial expressions that the interview was going the wrong way. So I asked
> them to show me some of their data definitions.
>
> It seems one of their billing tables allowed duplicate entries for orders.
> If you had two orders from different customers, or on different dates, or
> of different products, no problem. But you could have two identical
> entries in this table, witth the same date, product, and customer. They
> had
> no "order number" to tell the two entries apart.
>
> So I asked them, "If you get a complaint about a duplicate billing from a
> customer, how do you know whether your data entry clerk simply entered
> the same order twice, or whether the customer called in two separate
> orders on the same day?"
>
> "Funny you should ask that," came the answer. "We've never been able to
> figure that out in our system." "So we just issue a credit whenever the
> customers complain about duplicate billings."
>
> I didn't get the contract. The broker said the client had called me "too
> theoretical". The broker thought that meant "too expensive." They
> didn't
> want a computer consultant. They wanted a temp coder.
Wow. No order # just about takes the cake. Let me play I'll-top-that.
I once had a customer actually yell at me that his remote store had not uploaded invoices in a week, telling me point blank it was my fault. I don't like to get yelled at, and I knew my system worked, but I said I'd make the call. The conversation went something like this:
Me: When you send the Press button, what does it say?
Them: It says failed to connect.
Me: Hmmm, OK, what lights are on on the modem?
Them: Um, abc, xyz. (I can't remember the modem lights anymore)
Me: Hmmm, hit the button again, do you hear the modem making
those weird modem noises?
Them: Nope
Me: Do you hear it make a dial tone?
Them: Nope
Me: OK, let's figure out if it's plugged into the phone line.
Find the thin wire on the modem and tell me if it is plugged
into the wall.
Them: Nope, one end is in the modem, the other is on the floor. Me: Well, OK then, now we know we have to plug it in. Them: Oh we can't plug it in.
Me: ? Why not?
Them: They knocked out that wall last week.
-- Kenneth Downs Use first initial plus last name at last name plus literal "fam.net" to email meReceived on Sat Oct 09 2004 - 14:42:06 CEST