Re: Problem with n to n relation

Am Freitag, 5. Oktober 2001 14:30 schrieb Morgan Curley:
> 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 to
> your structure. Only one record can exist ffor a given person at a
> given address. However any person can have any number of address
> and any address can have any number of people living at it.

ok fine, i understood it after i figured out what pk means :-)

but how do i reach my goal. It should not be allowed to have a person
without any address??

janning

> At 12:39 PM 10/5/2001 +0200, Janning Vygen wrote:

> >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???