MVSFORUMS.com

[Naveen_jr777]

Hi,

Can we load VSAM - KSDS with the records sorted on DECENDING order on key.

If yes please let me know how to do it.

Thanks
Naveen.

[kolusu]

Naveen_jr777,

You canNOT. The Key is always in ascending sequence

kolusu
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Kolusu
www.linkedin.com/in/kolusu

[jsharon1248]

I know one way to accomplish the same thing if you have a numeric key. Subtact the key from all 9's when you load/retrieve it. Say you have 2 keys, 157 and 314. You would use 842 in place of the 157 value, and 685 in place of the 314 value. To convert it back, just subtract from all 9's again. 999-842 becomes 157 and 999-685 becomes 314. Things would get a lot more complicated trying to do this with alpha data, but I suppose it could be done.

[expat]

But why would you want to do that ???

Just sort the data from where ever straight into the VSAM file
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If it's true that we are here to help others,
then what exactly are the others here for ?

[jsharon1248]

Since you can't load records with a descending key, using this 9's complement technique will accomplish the same thing for numeric keys. I worked at a shop that utilized this technique with dates so that when they used skip sequential processing, the first record returned had the most recent date. The last record had the oldest. I don't know what the op was trying to accomplish.

[dbzTHEdinosauer]

jsharon1248,

you are still loading the vsam ksds with ascending keys.
_________________
Dick Brenholtz
American living in Varel, Germany

[jsharon1248]

Right. The 9's complement technique still loads the physical keys in ascending order, but the logical keys are descending. If we have customer, ABC, and they have 3 orders with dates 20070810, 20070821, and 20070822, just loading them as is will result in the following physical order:
ABC20070810
ABC20070821
ABC20070822

Apply the 9's complement technique to the dates and you get the following physical order:
ABC79929177 (99999999 - 20070822 = 79929177)
ABC79929178 (99999999 - 20070821 = 79929178)
ABC79929189 (99999999 - 20070810 = 79929189)

You're loading the 9's complement key in ascending order, but the actual dates they represent are in descending order. When you retrieve the dates, just apply the technique again; 99999999 - 79929177 = 20070822 and so forth,.

[dbzTHEdinosauer]

jsharon1248,

not even bothering to address the idiot issues of all input sorts being changed, all match merge compare logic being reversed, you missed the question:

[kolusu]

jsharon1248,

I think the 9's complement with dates is a little dangerous. for ex if for some reason the following numbers are stored in the file

[jsharon1248]

dbzTHEdinosaur

I didn't miss the original question. It was quite clear and the answer is no. You missed the point of my first post. I was presenting an option that might be suitable in some cases. The op didn't say what they were trying to do, so I was presenting a technique that I've seen used effectively. I don't know if it would work for them, but I thought maybe they'd find it useful.

To address the 'idiot' issue of sorting, you're still sorting the key in ascending sequence so I'm not sure how that changes. For the 'idiot' issue of matching and merging, as long as your files are consistent, both 9's complement or both original, you can still match and merge. And yes, any application that wants to access the VSAM file would need to be aware of the conversion.


kolusu
As long as you start with a valid date, you'll wind up with a valid date. The only way you'd get an invalid date on the conversion from 9's complement would be to convert an invalid date to 9's complement.

[Terry_Heinze]

The 1st time I ran into storing keys in 9s complement was in the case of storing the effective date of a price list file. This was many years ago and was used for an ISAM file (the precursor to VSAM). It was a very effective way, for its time, of accessing the most recent price list date, but of course nowdays there are better techniques.
_________________
....Terry

[jsharon1248]

Terry

Agreed. I wouldn't advocate 9's complement as a first choice. There are better options. But if the op has a VSAM requirement and no other choice, this might be a good fit.