[LeetCode]-DataBase-Customers Who Never Order

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

需求：查询没下单的客户

查询：

CREATE TABLE Customers(
Id TINYINT UNSIGNED,
Name VARCHAR(20)
)ENGINE=MyISAM CHARSET=utf8;

CREATE TABLE Orders(
Id TINYINT UNSIGNED,
CustomerId TINYINT UNSIGNED
)ENGINE=MyISAM CHARSET=utf8;

SELECT t1.Name
FROM Customers t1
WHERE NOT EXISTS(
SELECT * FROM Orders t2 WHERE t2.CustomerId=t1.Id
)

[LeetCode]-DataBase-Customers Who Never Order

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原文地址：http://www.cnblogs.com/lianliang/p/5303029.html