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🎨 视觉封面LeetCode Customers Who Never Order
Problem
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 |
+-----------+
即找到没有订单的客户
MySQL
解法一
SELECT Name AS Customers FROM Customers c WHERE c.Id NOT IN (SELECT CustomerId FROM Orders);
解法二
SELECT Customers FROM (SELECT c.Name AS Customers, o.Id AS oid FROM Customers c LEFT JOIN Orders o ON c.Id = o.CustomerId) AS r WHERE r.oid IS NULL;
分析
无
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