If you really need the behavior of two tables, you might consider looking at
inheritance.
I have something similar to your setup, and I use what Jan suggested. In my case, the tables "textfiles" and "binaryfiles" inherit from "files". My table "files" (and therefore the two children) contains a column "kind" that differentiates between the two children: it's a one-character field, constrained to be equal to either 't' or 'b'. In the children tables, I addded to that column a default value: 't' in one case and 'b' in the other.
It's not perfectly satisfactory, but it's the best I have found so far..