IDS Forum

Re: arithmetic function

Posted By: Art Kagel
Date: Saturday, 12 December 2009, at 11:26 p.m.

In Response To: Re: arithmetic function (Richard Snoke)

When a row is moved, say a variable length row moving due to outgrowing its
home page, it keeps its rowid, because the original slot location (which is
the actual address identified by the rowid) on the home page is replaced
with a forwarding pointer to the new location. However, if the table were
to be reorganized or altered with an operation that can't be performed in
place, or if a CLUSTERED index were to be (re)created on the table, then
most rows' rowids would indeed change, so ultimately you are correct, rowid
is a poor identifier for data except in the VERY short term.

Art

Art S. Kagel
Oninit (www.oninit.com)
IIUG Board of Directors (art@iiug.org)

See you at the 2010 IIUG Informix Conference
April 25-28, 2010
Overland Park (Kansas City), KS
www.iiug.org/conf

Disclaimer: Please keep in mind that my own opinions are my own opinions and
do not reflect on my employer, Oninit, the IIUG, nor any other organization
with which I am associated either explicitly or implicitly. Neither do
those opinions reflect those of other individuals affiliated with any entity
with which I am affiliated nor those of the entities themselves.

On Fri, Dec 11, 2009 at 4:02 PM, Richard Snoke <dsnoke@us.ibm.com> wrote:

> But rowids are not sequential integers, at least not in IDS. The real
> trick will be defining correct arithmetic on rowids (equality comparison
> and subtraction in this case). Given that rows can move around, I wonder
> how that might work. Anyone? It would be an interesting object (type and
> relevant methods.)
>
> It's a simpler problem if you're talking about the sequence of rows in an
> ordered result set, but still not trivial. An unordered result set
> (remembering that SQL results are not inherently ordered) is much harder.
>
> Cheers,
> Dick Snoke
> Executive IT Specialist
> IBM Software Group - ChannelWorks
>
> Tel: (404) 487-1595
> Email: dsnoke@us.ibm.com
>
> From:
> "DAVE GRIFFEN" <dgriffen@finishline.com>
> To:
> ids@iiug.org
> Date:
> 12/11/09 03:28 PM
> Subject:
> Re: arithmetic function [18362]
> Sent by:
> ids-bounces@iiug.org
>
> Gilles,
> If I understand your question correctly, you need to tie the table back to
>
> itself with a join criteria which will link to your definition of previous
>
> row. Something like...
>
> select a.rowid, a.value, a.value - b.value
> from mytable a, mytable b
> where a.rowid -1 = b.rowid
>
> --GILLES TCHAPPI
> --
> --Hi,
> --
> --Can someone please help.
> --Is there a way to retrieve the value of some column before/after the
> curent
> --column matching some 'where clause'. My goal is to retrieve in one shot,
>
> with
> --one 'select statement', for instance the value of the current row and
> the
> --difference (for the same column) between the value of the current row
> and
> the
> --value of the previous row ie for the same column : value of current row
> -
> value
> --previous row
> --
> --Regards
>
>
>
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>
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>
>
>
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Messages In This Thread

• arithmetic function
  GILLES TCHAPPI -- Friday, 11 December 2009, at 11:49 a.m.
  • Re: arithmetic function
    DAVE GRIFFEN -- Friday, 11 December 2009, at 3:27 p.m.
    • Re: arithmetic function
      Richard Snoke -- Friday, 11 December 2009, at 4:02 p.m.
      • Re: arithmetic function
        DAVE GRIFFEN -- Saturday, 12 December 2009, at 2:56 p.m.
      • Re: arithmetic function
        Art Kagel -- Saturday, 12 December 2009, at 11:26 p.m.
    • Re: arithmetic function
      Art Kagel -- Saturday, 12 December 2009, at 11:22 p.m.

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