Which is the way Oracle does multi column indexes by storing the data in
the index.
So a multicolumn index is by far faster in Oracle when you have an index
with
all the columns in it.

I guess hints (Plan) are very important in FB ;-) .

Aage Johansen wrote:

>Ann W. Harrison wrote:
> >
> > At 06:07 PM 9/30/2002 +0200, Martijn Tonies wrote:
> >
> > >Question: I tend to put the _most_ selective first to reduce index page
> > >reads and narrowing down any results from the index...
> > >Isn't this right?
> >
> > Nope. Firebird treats the whole index key as if it were a single
> > string of binary bytes. The only thing that affects the number of
> > index reads is the compressed length of the key. Leading duplicate
> > bytes disappear. ...
> > ...
>
>I've just "stolen" the following comment in a message today on b.p.i.sql:
>------------------------------
><<
>Experiences from my current project:
>
>If you use two columns to combine them in a compound index be careful if
>the first column has a very bad selectivity (many duplicate values).
>
>We all know that if you use a non compound index which has many dups on a
>specific value the lookup on one of those rows is getting slower the more
>dups you have.
>But this is also applicable for one column of a compound index.
>
>I our current project I could increase the speed by about 500 times for
>retrieving rows by doing the following:
>I defined an additional field which contains the values of the both columns
>in question stripped together by a trigger and defined a no compound index
>on that single column instead of the compound index on the both columns.
> >>
>------------------------------
>
>Doesn't this indicate that Martijn's way of defining multicolumn indexes is
>a good one?
>
>
>Regards,
>Aage J.
>
>
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--
Thomas Miller
Delphi Client/Server Certified Developer
BSS Accounting & Distribution Software
BSS Enterprise Accounting FrameWork

http://www.bss-software.com