Select Code to Download

create table baseitems (
        id integer primary key,
        data text
);

create table items (
        id integer,
...
        primary key (id, subid),
        foreign key (id) references baseitems (id)
);

create table codes (
        id integer,
...
        unique (id, subid, data),
        foreign key (id, subid) references items(id, subid)
);