NOT EXIST clause - sql

Question

I am trying to find Products that have never been ordered. My 2 tables look like this.
CREATE TABLE Orders
(OrderNum NUMBER(10) NOT NULL,
OrderDate DATE NOT NULL,
Cust NUMBER(10),
Rep NUMBER(10),
Mfr CHAR(3) NOT NULL,
Product CHAR(5) NOT NULL,
Qty NUMBER(5) NOT NULL,
Amount NUMBER(9,2) NOT NULL,
CONSTRAINT OrdersPK
PRIMARY KEY (OrderNum));
CREATE TABLE Products
(Mfr CHAR(3) NOT NULL,
Product CHAR(5) NOT NULL,
Description VARCHAR2(20) NOT NULL,
Price NUMBER(9,2) NOT NULL,
QtyOnHand NUMBER(5),
CONSTRAINT ProductsPK
PRIMARY KEY (Mfr, Product));
The code I currently have looks like this.
SELECT Mfr, Product
FROM Products
WHERE NOT EXISTS (SELECT Products.Mfr
FROM Orders, Products
WHERE Orders.Mfr = Products.Mfr);
Although I am not getting any errors there are also no results showing up.
**EDIT: There are 26 Products and 19 of them have been ordered. I am expecting to get 7 Results but I am getting 0.

Answer 1

You can use NOT EXISTS, but you need to compare both keys:
SELECT p.Mfr, p.Product
FROM Products p
WHERE NOT EXISTS (SELECT 1
FROM Orders o
WHERE o.Mfr = p.Mfr AND
o.Product = p.Product
);
This is a case where it makes lots of sense to have an auto generated primary key that can be used for foreign key relationships.

Answer 2

Try this one
SELECT Mfr, Product
FROM Products
WHERE NOT EXISTS (SELECT Orders.Mfr
FROM Orders
WHERE Orders.Mfr = Products.Mfr AND Orders.Product = Products.Product);

Answer 3

An alternative is to use the set operation operator EXCEPT - as you want "the set of Products that don't exist in Orders":
SELECT
Mfr,
Product
FROM
Products
EXCEPT
SELECT
DISTINCT
Mfr,
Product
FROM
Orders
You can then use this as a subquery to get full product information.
SELECT
*
FROM
Products
INNER JOIN (
SELECT
Mfr,
Product
FROM
Products
EXCEPT
SELECT
DISTINCT
Mfr,
Product
FROM
Orders
) AS ProductsWithNoOrders ON
Products.Mfr = ProductsWithNoOrders.Mfr AND
Products.Product = ProductsWithNoOrders.Product