Re: DBA Question

[Vernon Hamberg <vhamberg@xxxxxxxxxxx>]

As I see it, an OPNQRYF is more like the old logical file. If you use the 
KEYFLD parameter, you have a keyed logical. Whether you choose to use it as 
keyed depends on you - use 'K' on your F-spec, other ways in other languages.

The expression "non-keyed view" is redundant, in a way - a view never has a 
key. If you do a DSPFD of a view (try DSPFD QSYS2/SYSCOLUMNS), you will see 
"SQL file type" = VIEW, and then the CREATE VIEW statement that was used. 
That contains a SELECT statement. My observation is that the system runs 
that statement each time you use the view, even when you use it in RPG.

Also, if you look further down, it shows the "Access path" to be "Arrival" 
- yes, Martha, non-keyed files have an access path, too.   ;-)

As to a view being sequential, yes, maybe. But not guaranteed to be the 
physical ordering. If you have various parallel processes working on 
returning the data, results are unpredictable - different subsets can 
arrive anytime. Look at the SQL (Database) performance & optimization 
manual for more on access methods used by the SQL optimizer.

You CAN use an index in RPG - but you get no field selection, just order. 
You CAN use a view in RPG - but you get only field selection (albeit with 
possible calculated expressions, more flexible joining possibilities,etc.).

Clear as mud? Very thin mud?

HTH
Vern

At 12:30 AM 6/19/2005, you wrote:

> now I am confused again.  Isn't a non-keyed view treated as a sequential
> file?  In this scenario wouldn't a non-keyed view be more similar to an
> opnqryf?
>
>
>
> ---------------------------------
>
> Booth Martin
>
> http://www.martinvt.com
>
> ---------------------------------
>
> -------Original Message-------
>
>
>
> From: Midrange Systems Technical Discussion
>
> Date: 06/18/05 13:00:45
>
> To: Midrange Systems Technical Discussion
>
> Subject: Re: DBA Question
>
>
>
> Hi Jack,
>
>
>
> Others have highlighted quite a few of the similarities/differences. My own
>
> view (pardon the pun) is that it depends on how you intend to use them.
>
>
>
> If you are talking about developing a DB that will be accessed primarily by
>
> SQL from many different sources, then Views and Indexes. If it is primarily
>
> for RPG, then views, indexes and logical files.
>
>
>
> At its simplest, an index is a keyed logical and a view is a non keyed
>
> logical. From an RPG angle the problem is with the views - even they are a
>
> lot more powerful then DDS created logicals they are of little use in RPG
>
> since they do not have a key - so only useful if using embedded SQL.
>
>
>
> FWIW, I did an article on comparing DDS and SQL's DDL on search400 at
>
> http://search400.techtarget.com/tip/1,289483,sid3_gci1021854,00.html?FromTax
>
> onomy=%2Fpr%2F2f9
>
>
>
> HTH
>
>
>
> Paul Tuohy
>
>
>
> ----- Original Message -----
>
> From: "Jack Derham" <derhamj@xxxxxxxxxxxxx>
>
> To: "'Midrange Systems Technical Discussion'" <midrange-l@xxxxxxxxxxxx>
>
> Sent: Saturday, June 18, 2005 3:40 AM
>
> Subject: DBA Question
>
>
>
>
>
> > To the List,
>
>
>
>
>
>
>
> > Got into a discussion this afternoon about what the real differences are
>
> > between logical files, views and indexes. The discussion got a little
>
> heated
>
> > at times so I would ask that some of you well versed members to please
>
> help
>
> > out less fortunate uninformed members about the real physical and logical
>
> > attributes of these object types.
>
>
>
>
>
>
>
> > Jack Derham
>
>
>
> > Direct Systems, Inc.