Re: Do I need a PK on a join table?

David Portas wrote:

> Knut Stolze wrote:
>>
>> Well, you have to use _some_ mechanism on the internal layer to support
>> the logical constructs on the conceptual layer.
>
> Not always. Sometimes you don't want or need an index for every unique
> constraint. For example:
>
> If the key is a superkey with a candidate key already defined
> If check constraints prevent duplicates

You're right. I forgot about those as not many products actually support arbitrary check constraints.

> If constraints on views prevent duplicates
>
> You may still need the constraint to support a foreign key. You don't
> need the index.

You can use informational unique constraints for that.

-- 
Knut Stolze
DB2 Information Integration Development
IBM Germany