Chield Serial

Hi.
Is there a way to make a serial columm that works with father table???
I.e:I have created a table called "vending" and its chield table called "items".The items table have a serial columm,
butI need the serial colum starts with 0
 
for each vending.
create table vending ( id serial primary key,  --Ok, this serial: 0 - 9999xxx date_ date);create table items (
vending_idreferences vending, items_id   serial,  -- THIS SERIAL NEED to start 0 for each vending_id primary key
(vending_id,items_id));insertinto vending values (1,now());insert into vending values (2,now());insert into items
values(1);insert into items values (1);insert into items values (2);insert into items values (2);select * from items;
 
vending_id  |  items_id         1  |         1         1  |         2         2  |         3    <<=== Here! The
items_idneed to be 1 (start again
 
for each vending_id)         2  |         4    <<==
Thanks all.