• Subject: Re: PF File Definition questions...
  • From: "Ken Sims at SWS Nevada" <ken.sws@xxxxxxxxx>
  • Date: Fri, 15 Oct 1999 11:37:04 -0700

Hi Chuck -

>Date: Thu, 14 Oct 1999 14:59:42 +0100
>From: Chuck Lewis <clewis@iquest.net>
>Subject: PF File Definition questions...

>Is there something I'm missing when it comes to NOT having the "most
>common" field(s) in a PF defined in the PF a key field(s) ?

My feeling is that files that require uniqueness should have the physical
file keyed with the unique field(s) and UNIQUE specified.  All of the
logicals should have those field(s) as the last key field(s) to ensure
a consistence sequence regardless of the relative record number.  In
other words, all of the logicals will actually end up being unique keyed
as well, but don't actually specify UNIQUE.  It isn't needed because the
physical is enforcing uniqueness, and it would hurt performance as well.

History type files and other files that do not require uniqueness I
usually create with an unkeyed physical.  I try to create the logicals
with sufficient key fields to insure a consistent order, though that may
not always be possible at an absolute level (if it was, there would be
uniqueness, even if not enforced).

So my usual practice is:

1. only physical files are ever keyed UNIQUE.
2. physical files are either keyed UNIQUE or not keyed.
3. if there should be uniqueness, do enforce it with a uniquely
   keyed physical.
4. as much as possible, create logicals that will read in the
   same order regardless of relative record numbers.  (With a
   uniquely keyed physical, this is always possible.)

Everything else is just application of those principles.

Ken
Southern Wine and Spirits of Nevada, Inc.

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