in addition to the post from Thomas, it is good to know that QV automatically links tables together with common fieldnames (case sensitive). This is a very convenient and powerful feature, if you can handle it. But if you are not familare with it it may lead into funny and unexpected results. If you like you can post a first data-model you created to discuss it deeper.
Another point is that a QV-Join is not the same as a SQL-Join. See Manual (or in this forum, there is good stuff about these themes). Or even next post :-)
The main reason for that is for my oppinion because the fieldnames are unique through the whole application.