Problems creating table after normalisation - oracle

Question

I have been given a task to normalise a sales order, create a relational schema and input the data into SQL developer.
I have normalised to 3NF and got this:
Customer(Customer_ID, Customer_name) ... Primary key = Customer_ID
Employee(Employee_ID, Employee_name) ... Primary key = Employee_ID
Sales_Order(Sales_order_ID, Employee_ID, Customer_ID, Sale_date, Order_total) ... Primary key = Sales_order_ID ... Foreign keys = Employee_ID, Customer_ID
Order_Line(Sales_order_ID, Product_ID, Quantity, Line_total) ... Composite key = Sales_order_ID ... Foreign key = Product_ID
Product(Product_ID, Product_name, Product_price, Product_colour) ... Primary key = Product_ID
I then inputted the tables, this is my SQL:
CREATE TABLE EMPLOYEE(
Employee_ID CHAR(3),
Employee_name CHAR(20),
CONSTRAINT pk_Employee PRIMARY KEY (Employee_name)
);
CREATE TABLE CUSTOMER(
Customer_ID CHAR(5),
Customer_Name CHAR(20),
CONSTRAINT pk_Customer PRIMARY KEY (Customer_ID)
);
CREATE TABLE PRODUCT(
Product_ID CHAR(5),
Product_Name CHAR(30),
Product_Colour CHAR(10),
Product_Price CHAR(5),
CONSTRAINT pk_Product PRIMARY KEY (Product_ID)
);
CREATE TABLE SALES_ORDER(
Sales_order_ID CHAR(6),
Employee_ID CHAR(3),
Customer_ID CHAR(5),
Sale_Date CHAR(10),
Order_total CHAR(7),
CONSTRAINT pk_Order PRIMARY KEY (Sales_order_ID),
CONSTRAINT fk_Order FOREIGN KEY (Employee_ID) REFERENCES EMPLOYEE (Employee_ID),
FOREIGN KEY (Customer_ID) REFERENCES CUSTOMER (Customer_ID)
);
CREATE TABLE ORDER_LINE(
Sales_order_ID CHAR(6),
Product_ID CHAR(5),
Quantity CHAR(3),
Line_total CHAR(5),
CONSTRAINT pk_Order_Line PRIMARY KEY (Sales_order_ID),
FOREIGN KEY (Product_ID) REFERENCES PRODUCT (Product_ID)
);
I am able to input tables Employee, Customer, Product, Sales_order but unable to input Order_line
I am told that the table or view does not exist!
What does this mean?
Have I normalised incorrectly?
Have I designed the relational schema incorrectly?
Any help would be deeply appreciated

Answer 1

When I run your code in this db fiddle, creation of table SALE_ORDER fails with the following message:
ORA-02270: no matching unique or primary key for this column-list
This is because of this foreign key:
CONSTRAINT fk_Order FOREIGN KEY (Employee_ID) REFERENCES EMPLOYEE (Employee_ID),
The underlying problem is that you have defined Employee_name as the primary key of table EMPLOYEE.
CREATE TABLE EMPLOYEE (
Employee_ID CHAR(3),
Employee_name CHAR(20),
CONSTRAINT pk_Employee PRIMARY KEY (Employee_ID)
);
This does not seem like a sensible option. In the real life, it is possible that two different employees would have the same name. Instead, you probably want to use Employee_ID as the primary key for EMPLOYEE.
Consider this definition for table EMPLOYEE:
CREATE TABLE EMPLOYEE (
Employee_ID CHAR(3),
Employee_name CHAR(20),
CONSTRAINT pk_Employee PRIMARY KEY (Employee_ID)
);
With this new set up, all tables are created successfully. You may now insert your data.
Demo on DB Fiddle
Side note: I forsee issues with table ORDER_LINE:
primary key should be Order_line_ID instead of Sales_order_ID
Sales_order_ID should have a foreign key constraint referencing SALE_ORDER(Sales_order_ID).
Consider this new definition for ORDER_LINE:
CREATE TABLE ORDER_LINE(
Order_line_ID CHAR(6),
Sales_order_ID CHAR(6),
Product_ID CHAR(5),
Quantity CHAR(3),
Line_total CHAR(5),
CONSTRAINT pk_Order_Line PRIMARY KEY (Order_line_ID),
FOREIGN KEY (Product_ID) REFERENCES PRODUCT (Product_ID),
FOREIGN KEY (Sales_order_ID) REFERENCES SALES_ORDER(Sales_order_ID)
);