I have used FK in my database in these cases and I conccur in many points
with Geoff.
My only problem was a bad plan choiced by Interbase sometimes.
But, I work around this adding a complement to fields on select statement to
force interbase to use the correct plan.

Luiz.

----- Original Message -----
From: Geoff Worboys <geoff@...>
To: <IBObjects@yahoogroups.com>
Sent: Tuesday, April 03, 2001 11:55 AM
Subject: Re: [IBO] Foreign Key


> > This means, that performance-problems will only happen on insert,
> > update and delete and not for a select ?
>
> That depends on exactly how IB stores the index data in its data pages
> and I dont know the details - but I would expect *simple* selects to
> be mostly uneffected. In more complex selects (joins etc) there may
> be other issues.
>
>
> > What means high or low selectivity of a index ?
>
> How selective is the index when given a full input value (all fields
> of the index specified).
>
> A highly selective index will return very few records. For example
> the primary key always has maximum selectivity - it returns on only
> record for any given input. (IOW It is very selective.)
>
> A low selectivity index may return very many records. (IOW Its not
> very selective.)
>
>
> At what point low selectivity becomes a problem depends on many
> things, such as; how many records in the table, how large the
> database pages, how large the index values etc.
>
>
> HTH
>
> Geoff Worboys
> Telesis Computing
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>