RE: To Key or Not To Key a Physical

[Kurt Anderson <kurt.anderson@xxxxxxxxxxxxxx>]

I tried looking online for more information about how indexing occurs and couldn't pinpoint it.  

Maybe an example will help.
I want two keys over a file:
Key1: FieldA, FieldB
Key2: FieldB, FieldA

Option 1 is to have an arrival sequence Physical and 2 Logicals.
Option 2 is to key the Physical (let's say Key1) and then make a Logical, Key2.  

I've always preferred Option 2 for the simple reason of: hey, 2 files instead of 3; however I've been approached with the thought that Option2 will index over an index which would be less preferable to indexing over a non-keyed Physical.  Is this a valid concern?

Charles, you say that it's the general standard to always key the Physical.  I guess I'm looking for the reasoning behind that.

Thanks,
Kurt	

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Charles Wilt
Sent: Thursday, March 26, 2009 1:21 PM
To: Midrange Systems Technical Discussion
Subject: Re: To Key or Not To Key a Physical

Huh?

If you create a logical with the same access path as the physical, the
logical will share the PF access path.

Now-a-days, the recomendation is to always define a primary (aka
unique, non-NULL) key for the physical.

Charles

On Thu, Mar 26, 2009 at 2:13 PM, Kurt Anderson
<kurt.anderson@xxxxxxxxxxxxxx> wrote:
> If I'm going to have multiple logical files over a physical file, is it better to not key the physical file or is there no implication if I do key the physical file (and reduce the number of logicals needed by 1)?
>
> I'm not that familiar with how indexing works, and the concern is that a logical over a keyed physical will be indexing from an index.
>
> Thoughts?
>
> Thanks,
>
> Kurt Anderson
> Sr. Programmer/Analyst
> CustomCall Data Systems
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