Guido,

Strictly speaking foreign-keys do not need to be indices. The values
must be constrained to ensure that data integrity is maintained but
indexes are not required.

With IB v4.x (I think) it was decided that indexes would be
automatically created for foreign keys - to improve the performance of
cascade delete/update operations. However, it has been reasonably
suggested that this feature should be "disabled" since it can result in
very poorly structured indexes (typically they have a very low
selectivity - few values for a lot of rows) which significantly decrease
the performance of SELECTs and other common system operations.


Sean
-----Original Message-----
From: guido.klapperich@...
[mailto:guido.klapperich@...]
Sent: Wednesday, February 14, 2001 11:30 AM
To: ib-support@yahoogroups.com
Subject: Re: [ib-support] Is a joined query faster than a
subquery, or doesn't it matter?

> I read somewhere that Interbase creates an index automatic for

primary,

> foreign and unique keys.
>

Primary and Foreign-Keys ARE indices.


Guido



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