Listing A

create table orders

    (customer_id varchar(5) not null,
    
     order_date datetime not null,
     
     item_id varchar(5) not null,
     
     quantity int not null, 
     
     unit smallint default 1)
     
create table customers

    (customer_id varchar(5) not null unique,
    
     customer_name varchar(50) not null)
     
create table items

    (item_id varchar(5) unique,
    
     item_name varchar(20))