Miguel Vaz <pagongski@gmail.com> wrote:
> [...]
> * sites (generic):
> id_site
> name
> description
> x
> y
> * site_natural
> id
> id_site
> altitude
> * site_arqueology
> id
> id_site
> id_category
> id_period
> But i seem to be missing something. How can i have this in a way that its
> easy to list only "arqueology sites" for example. I feel the solution is
> simple enough, even for me, but its eluding me. Any help in the right
> direction would be very appreciated.
You mean archaeological sites that are not also natural
sites?
| SELECT * FROM site_arqeuology
| WHERE id_site NOT IN
| (SELECT id_site FROM site_natural);
There are numerous other ways to do this, i. e., with "LEFT
JOIN", "EXCEPT", etc.
Tim