Prev: Importing Tab Delimited Text File to an Existing Table in Access
Next: Table structure for separated families
From: QB on 22 Mar 2010 16:38
Correct me if I misunderstood, but I read that one should index fields that
are used as criteria in queries.

With this in mind, when one does a caculated field in a query using multiple
table fields, this means I should index each of these as well?

Ie:
(oldValue - newValue)/oldValue As PercentDiff

I should index oldValue and newValue?

Thank you,

QB
From: Jeff Boyce on 22 Mar 2010 17:03
.... it depends ... <G>

If your table has a few thousand rows, if your database isn't split, if you
only have one user at a time, ...
you might not need indexing.

If you have 100's of thousands of rows, if the back-end/data is on a slow
LAN, in a db server, if ...
you might need indexing.

What performance differences have you seen when you tried it?

Regards

Jeff Boyce
Microsoft Access MVP

--
Disclaimer: This author may have received products and services mentioned
in this post. Mention and/or description of a product or service herein
does not constitute endorsement thereof.

Any code or pseudocode included in this post is offered "as is", with no
guarantee as to suitability.

You can thank the FTC of the USA for making this disclaimer
possible/necessary.

"QB" <QB(a)discussions.microsoft.com> wrote in message
news:CB37E4D2-1CA8-467E-8DB8-F5D219748D50(a)microsoft.com...
> Correct me if I misunderstood, but I read that one should index fields
> that
> are used as criteria in queries.
>
> With this in mind, when one does a caculated field in a query using
> multiple
> table fields, this means I should index each of these as well?
>
> Ie:
> (oldValue - newValue)/oldValue As PercentDiff
>
> I should index oldValue and newValue?
>
> Thank you,
>
> QB


From: QB on 22 Mar 2010 18:46
So based on your post, it is a trial and error thing?!

Here is the scenario:
Access 2003
Split Db
No server, simply shared off of a NAS Drive -- Each user has the FE
10 or less users
biggest table currently hold 130K records but the db is growing steadily
(currently BE at 54MB) probably 75K-100K records a year to the biggest table.

I haven't had the chance to do testing on indexing, that is why I wanted to
get some advice on the matter before I try and delve into it. I don't want
to make useless mistake and am more than willing to learn form people such as
yourself (people with far more knowledge and experience on the matter).

Is there a drawback to indexing fields? What about indexing fields that
aren't used in queries as criteria (over-indexing)? Does indexing add load
to database processing (I'm assuming so or else you would have told me to
index to my heart's content :-) )?

Thank you,

QB





"Jeff Boyce" wrote:

> .... it depends ... <G>
>
> If your table has a few thousand rows, if your database isn't split, if you
> only have one user at a time, ...
> you might not need indexing.
>
> If you have 100's of thousands of rows, if the back-end/data is on a slow
> LAN, in a db server, if ...
> you might need indexing.
>
> What performance differences have you seen when you tried it?
>
> Regards
>
> Jeff Boyce
> Microsoft Access MVP
>
> --
> Disclaimer: This author may have received products and services mentioned
> in this post. Mention and/or description of a product or service herein
> does not constitute endorsement thereof.
>
> Any code or pseudocode included in this post is offered "as is", with no
> guarantee as to suitability.
>
> You can thank the FTC of the USA for making this disclaimer
> possible/necessary.
>
> "QB" <QB(a)discussions.microsoft.com> wrote in message
> news:CB37E4D2-1CA8-467E-8DB8-F5D219748D50(a)microsoft.com...
> > Correct me if I misunderstood, but I read that one should index fields
> > that
> > are used as criteria in queries.
> >
> > With this in mind, when one does a caculated field in a query using
> > multiple
> > table fields, this means I should index each of these as well?
> >
> > Ie:
> > (oldValue - newValue)/oldValue As PercentDiff
> >
> > I should index oldValue and newValue?
> >
> > Thank you,
> >
> > QB
>
>
> .
>
From: John W. Vinson on 22 Mar 2010 18:51
On Mon, 22 Mar 2010 13:38:05 -0700, QB <QB(a)discussions.microsoft.com> wrote:

>Correct me if I misunderstood, but I read that one should index fields that
>are used as criteria in queries.
>
>With this in mind, when one does a caculated field in a query using multiple
>table fields, this means I should index each of these as well?
>
>Ie:
>(oldValue - newValue)/oldValue As PercentDiff
>
>I should index oldValue and newValue?
>
>Thank you,
>
>QB

Indexing the underlying fields in a calculated expression will not help, if
you're applying criteria to PercentDiff: it will still have to retrieve all
the rows, do the calculation on all of them, and only then apply the
criterion.

If you find performance is unacceptable (try it first, you might be pleasantly
surprised), post back with the actual criterion you're using; it may be that
some alternative way of framing the question will allow you to search for all
NewValues based on some expression on OldValue. Failing that, this might be
one of the rare instances where it's appropriate to store a derived value.
--

John W. Vinson [MVP]
From: John W. Vinson on 22 Mar 2010 19:51
On Mon, 22 Mar 2010 15:46:01 -0700, QB <QB(a)discussions.microsoft.com> wrote:

>Is there a drawback to indexing fields? What about indexing fields that
>aren't used in queries as criteria (over-indexing)? Does indexing add load
>to database processing (I'm assuming so or else you would have told me to
>index to my heart's content :-) )?

Indexes speed data retrieval but they *slow* data insertion or updating (the
program must update not only the table but all the indexes that are touched by
a change of the data); there is also a limit of 32 indexes on any one table.
In addition indexes do take up room in the database, counting toward the
2GByte limit on the size of the database.

--

John W. Vinson [MVP]
 |  Next  |  Last
Pages: 1 2
Prev: Importing Tab Delimited Text File to an Existing Table in Access
Next: Table structure for separated families