Re: multi column foreign key for implicitly unique columns

On 8/18/2004 9:49 AM, Markus Bertheau wrote:

> В Срд, 18.08.2004, в 15:33, Jan Wieck пишет:
>
>> Meaning that not enforcing the uniqueness of those columns isn't an
>> option.
>
> The thing is that the columns _are_ unique, there's just no unique
> constraint on them. They are unique because there's a unique constraint
> on a subset of these columns. So no additional uniqueness enforcing
> needed.
>

Yes, you are right, a superset of columns of a unique constraint is
allways unique as well.

I assume it is performance why you are denormalizing your data?

However, Bruce, this should be on the TODO list:

* Allow foreign key to reference a superset of the columns
covered by a unique constraint on the referenced table.

Jan

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