Re: How long is long enough for primary key ?

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

On Oct 8, 4:20 pm, Frank van Bortel <frank.van.bor..._at_gmail.com> wrote:
> krisl..._at_gmail.com schreef:
>
> > Hi Mr Morgan,
> > Thank you for your answer.
>
> > Our Sales Order :
>
> > OrderID : Number(10) -> PK, Surrogate Key
> > CustRefPO : VARCHAR2(30), Unique Constraint => PO numbers from
> > customer.That would be Purchase Order references, not PO numbers.
> If they are numbers, store them in a number column.
>
>
>
> > Yes, we just know that maximum is 30 chars, but there could be variants
> > of length because it comes from customers. And during payment (and also
> > other process the user will refer to this PO Numbers, not the PK.
>
> > Would it be performance issue here ?Where?
> How do you plan to use this? Do you know how an index scan
> (binary search) works? Or an index range scan?
> You will soon notice, there is no theoretical difference
> between such searches, based on the data type to be searched.
>
> In practice, well, as Daniel Morgan indicated, there are suspicions
> that numbers compare faster.
>
> I suspect performance differences will be measurable, at best. Not
> noticeable. Build a test case around it - you should be able to
> produce results in a matter of minutes.
>
> About 85% of all performance issues I have ever seen, found their
> roots in a bad design.
> Some 10% found their cause in grossly underpowered systems (think
> parameters, memory assigned, etc) , and the rest was due to bugs.
>
> As a last remark: as PO reference is unique (are you sure? I tend
> to think Customer/PO Ref would be unique), why not use that for
> PK? Adding an extra index (PK + UK) will cause extra overhead on
> inserts, which will affect performance negatively.
> That is - if you plan on using a unique index (which I think
> you will)
> --
> Regards,
> Frank van Bortel
>
> Top-posting is one way to shut me up...
Received on Sun Oct 08 2006 - 20:33:15 CDT