  
 create table product_class(
 prod_cno number(11) primary key ,
 prod_cname varchar2(35),
 description varchar2(100) );
----------------------------------------------------------------------------
 
create table product(
prod_cno number(11) references product_class ,
prod_no number(11) primary key ,
prod_name varchar2(35),
qty number(11) ,
price number(11,2) ,
sup_co number(11) references supplier_class,
description varchar2(100) );
------------------------------------------------------------------------------
------------------------------------------------------------------------------
  
create table invoice(
inv_no number(11) primary key,
inv_date date,
cust_no number(11),
sum_inv number(11,2) );
------------------------------------------------------------------------------
  
create table invd(
inv_no number(11) references invoice,
prod_no number(11),
prod_name varchar2(35),
qty number(11),
price number(11,2),
sum_prod number(11,2) );