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  3. May 2019

Re: sql identity column generate always (WHY HAVE TO RESET)


what about my even better question Craig?
How to detect?


Hi Jay,

I spent quite a lot of time trying to figure out why I was getting
duplicates when I first started using these.

Eventually I realised and proved the issue was CPYF.
In my particulary case, I'd create the file with an IDENTITY and do a load
of testing in a DEV environment and when I was happy, move it up to TST.
If it was a file which required some static data - then I'd CPYF the
records from my DEV environment up to TST.

Often I wouldn't see the problem at first because the new file was created
and ready to start creating records with ID = 1 and from all of my testing
in DEV, the early records had been deleted, so maybe the first ID value
copied from DEV to TST was something like 12.
So My TST version would run fine and dandy until I got to the 12th record,
which would fail due to a record CPYF'd from DEV already having that ID.
But the 13th might work because it happened that my testing had removed
that value from DEV, maybe everything would look fine for a couple of
inserts and then I'd hit another duplicate. Confusing at first.

Once I learned only to insert records into these tables with RLA in a
program or SQL (omitting the ID column) I never had a problem.

With regard to your question though - sorry I haven't had occasion to
figure out where the next value is stored.
I've kicked the next value on using ALTER TABLE T ALTER COLUMN ID RESTART
with N etc but I'm sure you are aware of this.

Also I guess if you are using these you have come across
identity_val_Local() which you can use to determine the ID of the record
your process just wrote.
But I couldn't immediately see another function that might retrieve the
"next" ID value, although in practice by the time you retrieve that value
it might be out of date.

I had a quick look in SYSCOLUMNS and the info doesn't seem to be there so
I'm sorry I'm not sure how you would run a check.
I'd be interested to see if anyone knows where to get that info but I don't
have time just at the moment to go digging.

regards,
Craig

On Fri, 24 May 2019 at 14:38, Jay Vaughn <jeffersonvaughn@xxxxxxxxx> wrote:

what about my even better question Craig?

How to detect?

On Fri, May 24, 2019 at 9:32 AM Craig Richards <craig@xxxxxxxxxxxxxxxx>
wrote:

CPYF probably - it will keep ID from from_file and not increment ID in
to-file

On Fri, 24 May 2019 at 14:26, Jay Vaughn <jeffersonvaughn@xxxxxxxxx>
wrote:

id BIGINT NOT NULL GENERATED ALWAYS AS IDENTITY
(START WITH 1 INCREMENT BY 1)
primary key(id)

We all know that sometimes the identity column gets "out of whack" and
that
we have to reset it with the alter/restart...

My question is why does it get out of whack.
Even better question, how can we detect the presence of the out of
whackness before we are faced with a "attempt to write duplicate"
because
it was "out of whack"?
Is there a system table we can query to look at to detect these time
bombs?

Abused google looking for an answer and everyone prides themselves with
how
to restart it... and never is it explained how to detect them
beforehand.

TIA

jay
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