RE: Difference between Select and Omit in LF

[Ken Sims <mr3111@xxxxxxxxx>]

Hi Fred -

> Could this be the difference:
>
> Index size  . . . . . . . . . . . . . . :                    1056768
>
> vs:
>
> Index size  . . . . . . . . . . . . . . :                      24576

You can't just change S to O and reverse the comparison to get the equivalent.

The one logical is including records where PSATFG = 'A' *OR* PSSTCD < '30'
the other is including records where PSATFG = 'A' *AND* PSSTCD < '30'

If the selections are actually equivalent, the use of S vs O makes no 
difference.  I don't remember where I saw it, but internally the omits are 
converted to selects anyway.

Ordering is another matter (and another opportunity to create a logical 
that isn't actually equivalent if you have a mixture of S/O or 
and/or).  This is only going to matter when adding/changing 
records.  Performance will benefit, albeit probably not very much, by 
listing the most exclusive (in terms of the number of records) comparison 
first.

--
Ken
http://www.ke9nr.net/
Opinions expressed are my own and do not necessarily represent the views of 
my employer or anyone in their right mind.