Subject Re: [firebird-support] Unique constraint vs unique index, why do they have to be different?
Author Elmar Haneke
Helen Borrie schrieb:

> Because an index is not a constraint and a constraint is not an index. A
> constraint has rules, one of which is that it requires a unique index to
> enforce a rule.

There is one flaw hera: When trying to create an FK to fields having
an unique index only you get an error mesage indicating that an unique
index is required. This message should be changed to indicate an
unique constraint to be required - else it is rather confusing.