Leetcode183. 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 |
+———–+

大意就是找出另一张表不存在的

select Name as Customers 
from 
Customers c
where c.ID
not in 
(SELECT CustomerId FROM Orders o)