LeetCode（183）：从不订购的客户 Customers Who Never Order（SQL）

2019.12.10 LeetCode 从零单刷个人笔记整理（持续更新）

github：https://github.com/ChopinXBP/LeetCode-Babel

传送门：从不订购的客户

某网站包含两个表，Customers 表和 Orders 表。编写一个 SQL 查询，找出所有从不订购任何东西的客户。

Customers 表：

+----+-------+
| Id | Name  |
+----+-------+
| 1  | Joe   |
| 2  | Henry |
| 3  | Sam   |
| 4  | Max   |
+----+-------+

Orders 表：

+----+------------+
| Id | CustomerId |
+----+------------+
| 1  | 3          |
| 2  | 1          |
+----+------------+

例如给定上述表格，你的查询应返回：

+-----------+
| Customers |
+-----------+
| Henry     |
| Max       |
+-----------+

---

SELECT Name AS 'Customers'
FROM Customers c
LEFT OUTER JOIN (
    SELECT DISTINCT CustomerID AS 'cId'
    FROM Orders
) o
ON c.Id = o.cId
WHERE cId IS NULL;

SELECT Name AS 'Customers'
FROM Customers c
WHERE c.Id NOT IN (
    SELECT DISTINCT CustomerID AS 'cId'
    FROM Orders
);

SELECT c.Name AS 'Customers'
FROM Customers c
WHERE NOT EXISTS (
    SELECT 1
    FROM Orders o
    WHERE o.CustomerID = c.Id
);

---

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