Could you please help me with the following problem? I'm a total novice in DB design.
I have a table with researchers who visit our university. They come for some period of time (from, till). Now, how can I save in the database if somebody came several times? I have an entry already for a particular person and need to add some other stays and be able to see them in a form.
My idea was: this must be a many-to-many relationship. Ok. Then I need a third table Researcher/Stay. And then I don't know what to do next. In Stay-table "from+till" is a key. I haven't seen examples with double-value key in a many-to-many relationship and don't know what to do next.