gistfile1.sql

create table addresses (
    id serial primary key
);

create table street_addresses (
    id integer primary key references addresses(id),
    postal_code text not null,
    street text not null
    -- etcetera
);

create table po_box_addresses (
    id integer primary key references addresses(id),
    postal_code text not null,
    po_box_number text not null
    -- etcetera
);