just get rid of the serial_id in person2adress -- there is no reason for it.
Make the pk of that table a composite --> person_id, address_id <-- that way you have added some additional integrity
toyour structure. Only one record can exist for a given person at a given address. However any person can have any
numberof address and any address can have any number of people living at it.
Morgan
At 12:39 PM 10/5/2001 +0200, Janning Vygen wrote:
>Hi,
>
>i create n to n relations like this, right?
>
>create table person (
> id serial,
> name text
>);
>
>create table address (
> id serial,
> street text
> ...
>);
>
>create table person2adress (
> id serial,
> person_id integer not null references person(id),
> address_id integer not null references address(id),
>);
>
>than i can select all adresses from one person with id =1 with
>select street
>from address
>where id =
> (
> select adress_id
> from person2adress
> where person_id = 1
> );
>
>ok so far so good. but you can still insert persons without any
>adress. so its a 0..n relation. But how van i achieve that you can´t
>insert any person without adress???
>
>thanks in advance
>janning
>
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Morgan Curley
Partner, e4media
mcurley@e4media.com
917 751 8328
http://www.e4media.com
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