inheritance

Hello,

I am working with PostgreSQL 7.2.1 under Windows 2000 (native version by
  PeerDirect) and have a problem with inheritance. To illustrate it, I
will take the inheritance example from the Users Guide with a minor
change, i.e. I introduce a PRIMARY KEY to the original table cities.

CREATE TABLE cities (
     name            text PRIMARY KEY,
     population      float,
     altitude        int     -- (in ft)
);

CREATE TABLE capitals (
     state           char(2)
) INHERITS (cities);

My problem now is the following: If I insert a data set into capitals,
everything looks fine and a SELECT on cities returns the appropriate
data just inserted into capitals. But if I now insert a city with the
same name into cities the system will accept it so that I find myself
with two entries in cities that have the same PRIMARY KEY. Of course
this causes trouble, e.g. if I want to UPDATE one entry, an error
message appears. If I still insist on changing the entry, both will be
affected, because they share the same PRIMARY KEY.
Can anybody tell me how to solve this problem? Maybe it has already been
solved and is just a result of me using the old 7.2.1 version. I'd be
very grateful for any hints, since the inheritance features of
PostgreSQL would make life a lot easier for me.

Thanks for your help, Volker.

--
Volker Krey
v.krey@fz-juelich.de