Re: Advice on key design - Mailing list pgsql-sql

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
>
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