[LeetCode][SQL]Customers Who Never Order

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       |
+-----------+

https://leetcode.com/problems/customers-who-never-order/

---

好久没写SQL一下子忘记is null这个东西了，= null并没有用。

select Name as Customers from Customers left join Orders on Customers.Id = Orders.CustomerId where CustomerId is null

 

转载于:https://www.cnblogs.com/Liok3187/p/4508044.html