Foreign Key Question

[Stephan Szabo]

Inventory, Productnr, Productserial
(PK Inventory, Prouctnr)
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).

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[Bruno Wolff III]

On Mon, Feb 09, 2004 at 08:59:12 +0100,

Inventory, Productnr, Productserial
(PK Inventory, Prouctnr)
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?

Having typos in what you show us doesn't help.

Inventory, Productnr being unique does not imply Productnr is unique.
If Productnr in table 1 is unique, you should make a unique constraint
on it. If it isn't unique you can't use a foreign key reference and you
will need to write your own trigger functions to do whatever makes sense
for your problem.

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