CUSTOMER table
SQL> create table customer
2 (customer_no char(6) not null,
3 name varchar2(30) not null,
4 address varchar2(50) not null,
5 credit_limit number(6,2),
6 constraint customer_customer_no_pk primary key (customer_no));

Table created.

SALESMAN table
SQL> create table salesman
2 (salesman_id char(8),
3 name varchar2(20) not null,
4 address varchar2(50) not null,
5 emaill_address varchar2(30),
6 constraint salesman_salesman_id_pk primary key (salesman_id));

Table created.

ITEM table
SQL> create table item
2 (ISBN char(13) not null,
3 title varchar2(30) not null,
4 price number(4,2) not null,
5 constraint item_ISBN_pk primary key (ISBN));

Table created.

INVOICE table
SQL> create table invoice
2 (invoice_no char(1) not null,
3 invoice_date date not null,
4 salesman_id char(8),
5 customer_no char(6) not null,
6 ISBN char(13) not null,
7 Nos varchar2(2) not null,
8 credit_limit number(6,2),
9 payment_type varchar2(6) not null,
10 constraint invoice_invoice_no_pk primary key (invoice_no),
11 constraint invoice_salesman_id_fk foreign key (salesman_id)
12 references salesman(salesman_id),
13 constraint invoice_customer_no_fk foreign key (customer_no)
14 references customer(customer_no),
15 constraint invoice_ISBN_fk foreign key (ISBN)
16 references item(ISBN));

Table created.

DELIVERY table
SQL> create table delivery
2 (invoice_no char(1) not null,
3 ISBN char(13) not null,
4 constraint delivery_invoice_no_ISBN_cpk primary key (invoice_no,ISBN),
5 constraint delivery_invoice_fk foreign key (invoice_no)
6 references invoice(invoice_no),
7 constraint delivery_ISBN_fk foreign key (ISBN)
8 references item(ISBN));

Table created.

ORA-00001: unique constraint (SYSTEM.INVOICE_INVOICE_NO_PK) violated