Agreed with Anton, as PK, lpp_id is easier to be managed than (lpp_person_id + lpp_language_id) One more suggestion, foreign key constraints could be setup on lpp_person_id and lpp_language_id to link with target tables.
Thanks, Stan 2013/7/24 Anton Gavazuk <antongava...@gmail.com> > 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 <jorgemal1...@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 <antongava...@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 <jorgemal1...@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 >> > >> > >> > >> > >> > >> > >> > >
