Re: AW: READE with partial key

[Vernon Hamberg <vhamberg@xxxxxxxxxxxxxxx>]

FYI - in case someone didn't know how READE worked (I had a 
misconception until working with Open Access for database).

READE is a READ, then test for Equal.

That means the file is read in its order, as Birgitta, et al., have 
said. Then the key fields are compared against the partial key values 
you provide.

This is maybe obvious, but somehow the details were not to me. It came 
out when I tried to handle a situation where I changed the partial key 
value midstream. I had thought the process would reposition according to 
those values. Of course, that's a CHAIN or SETLL, now that I've thought 
back on it.

But in an OA handler, I had to do this the right way. Getting into the 
nitty-gritty was definitely interesting!

Why would a person do this? I don't know that I had a scenario, just 
that it was possible and I had to handle it. I suppose something like 
skip-processing - get the first of each group of some kind. Hey, do 
level checks rear their ugly head here?

HTH
Vern

On 6/20/2013 12:12 AM, Birgitta Hauser wrote:
> Contrary to SQL native IO always uses the predefined access path, i.e. the
> access path located within the DDS described files or SQL Indexes that are
> specified within the F-Specs.
> No additional optimization occurs.
> In this way reading with a partial key, will read the records according the
> key definition (i.e. in your case ascending date).
>
> Mit freundlichen Grüßen / Best regards
>
> Birgitta Hauser
>
> "Shoot for the moon, even if you miss, you'll land among the stars." (Les
> Brown)
> "If you think education is expensive, try ignorance." (Derek Bok)
> "What is worse than training your staff and losing them? Not training them
> and keeping them!"
>
> -----Ursprüngliche Nachricht-----
> Von: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] Im
> Auftrag von Jeff Crosby
> Gesendet: Wednesday, 19.6 2013 20:54
> An: RPG programming on the IBM i / System i
> Betreff: READE with partial key
>
> Suppose I have a file defined via DDL with unique key consisting of
>
> Item (ascending)
> Date (ascending)
>
>
>           // Set position in file
>           SETLL Item FILE;
>
>           // Only while this item
>           Dow '1';
>
>             Reade Item FILE;
>             If %EOF(FILE);
>               Leave;
>             Endif;
>
>             process record . . .
>
>           Enddo;
>
> I am not assured of getting records within this item in ascending Date
> sequence, am I?  Some testing I'm doing now shows that I don't.
>
>
>
> --
> Jeff Crosby
> VP Information Systems
> UniPro FoodService/Dilgard
> P.O. Box 13369
> Ft. Wayne, IN 46868-3369
> 260-422-7531
> www.dilgardfoods.com
>
> The opinions expressed are my own and not necessarily the opinion of my
> company.  Unless I say so.
> --
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