The reason is simple - as you need the artificial PK lpp_id, then
everything else becomes an constraint
Thanks,
Anton
On Jul 24, 2013, at 0:28, JORGE MALDONADO <jorgemal1960@gmail.com> wrote:
>> In your case it would be lpp_id as PK, and
>> lpp_person_id,lpp_language_id as unique constraint
>>
>> Thanks,
>> Anton
Is there a reason to do it the way you suggest?
Regards,
Jorge Maldonado
On Tue, Jul 23, 2013 at 5:02 PM, Anton Gavazuk <antongavazuk@gmail.com>wrote:
> Hi Jorge,
>
> In your case it would be lpp_id as PK, and
> lpp_person_id,lpp_language_id as unique constraint
>
> Thanks,
> Anton
>
> On Jul 23, 2013, at 23:45, JORGE MALDONADO <jorgemal1960@gmail.com> wrote:
>
> > I have 2 tables, a parent (tbl_persons) and a child
> (tbl_languages_per_person) as follows (a language table is also involved):
> >
> > ------------------
> > tbl_persons
> > ------------------
> > * per_id
> > * per_name
> > * per_address
> >
> > --------------------------------------
> > tbl_languages_per_person
> > --------------------------------------
> > * lpp_person_id
> > * lpp_language_id
> > * lpp_id
> >
> > As you can see, there is an obvious key in the child table which is
> "lpp_person_id + lpp_language_id", but I also need the field "lpp_id" as a
> unique key which is a field that contains a consecutive number of type
> serial.
> >
> > My question is: what should I configure as the primary key,
> "lpp_person_id + lpp_language_id" or "lpp_id"?
> > Is the role of a primary key different from that of a unique index?
> >
> > With respect,
> > Jorge Maldonado
> >
> >
> >
> >
> >
> >
>