RE: CHAIN Versus SETLL and READ When Data Needed

That's an interesting idea, to use the key data structure.  That
actually has never occurred to me.  I'm going to examine this idea more
because I think it would be a good way to maintain the keys than what I
typically do.



-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Barbara Morris
Sent: Wednesday, February 28, 2007 6:55 PM
To: rpg400-l@xxxxxxxxxxxx
Subject: Re: CHAIN Versus SETLL and READ When Data Needed

Shannon O'Donnell wrote:

              Key1    Klist
                          Kfld              Fld1
                          Kfld              Fld2
                          Kfld              Fld3
              Key2     Klist
                          Kfld              Fld1
                          Kfld              Fld2

CHAIN does seem better if you are always going use the data from a found

record.  But don't take my opinion too seriously because I'm not expert 
in the database; maybe there are scenarios (such as sparse keys) where 
SETLL is faster than CHAIN (or vice versa) when the record is not found.

  (Although a later post in this thread quotes from the manual saying 
that sometimes a CHAIN is faster than a SETLL with sparse keys ...)

Aside from the CHAIN vs SETLL issue, you can improve your key lists by 
using a key data structure, and then using %KDS(keyds:3) or 2 or 1.  (It

would be more self-documenting than the KLISTs, even aside from your 
somewhat devious use of Key1 as the name for the 3-key klist and Key3 as

the name for the 1-key klist :)  You could use a list of keyfields like 
Dennis suggested; but I think the keyds is _slightly_ better than a list

of keyfields _in this case_, since it's a bit easier to see that the 
same key ds is being used for each CHAIN in the group (only one name to 
check vs a list of 3 names or values).

D keyds         e ds        extname(file:*key)
  /free
    keyds.fld1 = something;
    keyds.fld2 = somethingelse;
    keyds.fld3 = whatever;
    chain %kds(keyds:3) file;
    if %found
       ...
    else;
       chain %kds(keyds:2) file;
       if %found
           ...
       else;
          chain %kds(keyds:1) file;