Re: Foreign Key Question

On Mon, 9 Feb 2004, Tuan Luu wrote:

> Example:
>
> Table 1:
> Inventory, Productnr, Productserial
> (PK Inventory, Prouctnr)
>
> Table 2:
> Pruductnr, Produktdesc, Productversion
> (PK Productnr; FK Productnr)
>
> This Construct gives me an error during the creation in Postgresql
> (saying there is no unique constraint matching given keys for referenced
> table xxxx). The Primary Key in table 1 consists of two columns. In the
> second table there is a foreign key refencing to the first table.
>
> A unique constraint doesn't make sense on table one. Am I missing
> something here?

What are the semantics you are looking for?  Foreign keys only can refer
to unique things, because except for a few odd cases involving nulls and
match partial, it's intended that one particular row is being referenced.
If there are multiple rows in table1 with a particular productnr, how do
you want a reference to that to act (esp in the case of delete or update
to table 1).