Subject RE: [IB-Architect] computed by index
Author David Schnepper
Deej implemented expression indices around 1993/1994. But they were
never turned on due to lack of QA time to test them. The
feature was passing all of his engineering tests.

I even recall adding something to it (even though the code wasn't fully
active). The part that recognizes an expression that could be
optimized by an index wasn't recognizing "a+b" as the same as "b+a".
Anway, my point is the code was fairly complete, and that lack-of-time
issues was the only thing that prevented it from shipping years ago.

This would be a great project for some firebird contributor - turn
on the code and see where you can go with it.


-----Original Message-----
From: Ann W. Harrison [mailto:aharrison@...]
Sent: Wednesday, March 06, 2002 8:12 AM
Subject: Re: [IB-Architect] computed by index

At 05:00 PM 3/6/2002 +0100, Nando Dessena wrote:
> > I know, IB can't create index for a computed by column.
> > I see, but WHY CAN'T?
>because a computed column isn't stored and thus it cannot be indexed.

There is a think called an expression index which is used
in some PC databases. Most of the code exists in the
engine to create & manage them, from back in the bad old
days where we were trying for complete dBase emulation.

Indexing computed fields is more of a problem because computed
fields can be volatile. The examples that László gave could
be handled by expression indexes.


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