Re: 1:c - relation in oracle

From: Christian Nein <christian_at_nein.de>
Date: Tue, 23 Dec 2003 15:02:20 +0100
Message-ID: <bs9hoh$1qo$02$1@news.t-online.com>

> Er.. since when does the N part in 1:N not mean 1:2? Or 1:1? Or 1:2?
>
> Or did you mean 1:3? Well, N can also be 3. Here ya go. N := 3. Thus 1:N
is now 1:3.
>
> That is why it is called a 1:N relationship.
>
> N can even be c. N := c. Now 1:c is also realised.
>
> Entity relationships are either a 1:N or N:M. Show me one that is not.
>
> --
> Billy

I think you got me wrong. Here is an example of what I mean:

Let's say we have 2 tables, one containg INVOICES and a second one containg the associated INVOICE LINE ITEMS

case 1)
A relation shall ensure that each INVOICE exactly has 2 INVOICE LINE ITEMS (not 0 or 1 or 3 or 4 or ...)

case 2)
A relation shall ensure that each INVOICE has maximal one (0 or 1) INVOICE LINE ITEMS How can I define these relations without using triggers?

Christian Received on Tue Dec 23 2003 - 08:02:20 CST