Customers Who Never Order

Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything.

Table: Customers.

Id	Name
1	Joe
2	Henry
3	Sam
4	Max

Table: Orders.

Id	CustomerId
1	3
2	1

Using the above tables as example, return the following:

Customers
Henry
Max

解法：

SELECT Name AS Customers FROM Customers 
WHERE Id NOT IN (
    SELECT CustomerId AS Id FROM Orders
)

另一个解法

左连接只含有自己原有的部分。

SELECT Name AS Customers FROM Customers
LEFT JOIN Orders ON Customers.Id = Orders.CustomerId 
WHERE CustomerId IS NULL