Re: Alternate keys.

In article <39F08952.9BC60BC8_at_home.nl>,
  frank <fbortel_at_home.nl> wrote:
> In the purest sense, Order No is not a primary identifier. (I reserve
> the work 'key' for a technical implementation - data modeling does
> not care about technical implementations).
> Order No is a result of a technical implementation: the need to be
> able to identify a particular order fast - computers are fast with
> numbers, so let's give it a number.
>
> The primary (or: unique) identifier is probably a combination of
> customer name, cust. address, products ordered, date ordered.

Order No would be an appropriate primary key if it uniquely identifies a table row.

> As you can see, you will need a lot of "real world" things to identify
> a particular order. Better introduce a number - a primary key on a
table.

Why introduce a sequence when you already have an appropriate key.

> BTW: customer would be a better example: people never refer to, or are
> referred to by numbers, always by name.

What if you have two customers with the same name?

Sanrenkur

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Before you buy. Received on Fri Oct 20 2000 - 13:38:08 CDT