Outer Join and a two step query

[Jon]

Hi,
I need to list which dog breeds have never been sold at the Store by using
Outer Join and a two step query. Anyone can explain for me Out join

Thank you all

My tables are as follows:
Table Animal has
AnimalID
Category
Breed

Table Customers
CustomerID
Phone
Name

Table Sales
CustomeriD
SaleDate
SaleID

Table Saleanimal
SaleID
AnimalID
SalePrice

Table SaleItem
SaleiD
ItemID

 

[Douglas J. Steele]

The following SQL should list which dogs have not been sold at the store:

SELECT Animal.AnimalID, Animal.Category, Animal.Breed
FROM Animal LEFT JOIN Saleanimal
ON Animal.AnimalID = Saleanimal.AnimalID
WHERE Saleanimal.AnimalID IS NULL

Another, less efficient, approach would be

SELECT AnimalID, Category, Breed
FROM Animal
WHERE AnimalID NOT IN
(SELECT DISTINCT AnimalID
FROM Saleanimal)