Re: How long is long enough for primary key ?

EdStevens wrote:
> krislioe_at_gmail.com wrote:
> > Hi,
> > Thank you for your response.
> >
> > > why not use that for PK?
> > >Adding an extra index (PK + UK) will
> > >cause extra overhead on inserts, which
> > >will affect performance negatively.
> >
> > I don't use PORef as PK , because the user should be able to change it.
> > That is the reason.
> >
> > I have no other choice but using PK+UK, do I ?
> >
> > Thank you,
> > xtanto
> >
> <snip>
>
> Interesting. If the PORef is user (customer?) supplied, and you define
> it as unique, how do you guarantee that customer "A" doesn't supply the
> same PO# as customer "B"?

Not only that, how do you know customer A isn't going to supply the same PORef as customer A? Silly as it sounds out of context, many commercial ERP system have company or divisional attributes as part of a compound key, but users don't necessarily tell their vendors that. Also, some people haven't mentally moved into the computer age, so every PORef might be "Per Susan." You (xtanto) might consider a non-unique customer+PORef key.

jg

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