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