LeetCode | 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       |+-----------+

想到两种方法：left join，not in。

not in：

select Customers.Name  

from Customers 

where  Customers.Id not in (select distinct CustomerId from Orders);

left join：

SELECT Name 

FROM Customers c LEFTJOIN Orders o ON c.Id = o.CustomerId 

WHERE o.Id ISNULL;

在网上还看见一种方法：not exists:

SELECT Name FROM Customers c 

WHERENOTEXISTS (SELECT CustomerId FROM Orders o WHERE o.CustomerId = c.id);