首页 » 数据库 » MsSql

SQL实现LeetCode(183.从未下单订购的顾客)

MsSql 2022-01-09

[LeetCode] 183.Customers Who Never Order 从未下单订购的顾客

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       |
+-----------+

这道题让我们给了我们一个Customers表和一个Orders表,让我们找到从来没有下单的顾客,那么我们最直接的方法就是找没有在Orders表中出现的顾客Id就行了,用Not in关键字,如下所示:

解法一:

SELECT Name AS Customers FROM Customers 
WHERE Id NOT IN (SELECT CustomerId FROM Orders);

或者我们也可以用左交来联合两个表,只要找出右边的CustomerId为Null的顾客就是木有下单的:

解法二:

SELECT Name AS Customers FROM Customers
LEFT JOIN Orders ON Customers.Id = Orders.CustomerId
WHERE Orders.CustomerId IS NULL;

我们还可以用Not exists关键字来做,原理和Not in很像,参见代码如下:

解法三:

SELECT Name AS Customers FROM Customers c
WHERE NOT EXISTS (SELECT * FROM Orders o WHERE o.CustomerId = c.Id);

参考资料:

https://leetcode.com/discuss/22624/three-accepted-solutions

https://leetcode.com/discuss/53213/a-solution-using-not-in-and-another-one-using-left-join

到此这篇关于SQL实现LeetCode(182.从未下单订购的顾客)的文章就介绍到这了,更多相关SQL实现从未下单订购的顾客内容请搜索www.580doc.com以前的文章或继续浏览下面的相关文章希望大家以后多多支持www.580doc.com!


上一篇:SQL实现LeetCode(184.系里最高薪水)下一篇:SQL实现LeetCode(182.重复的邮箱)
程序园_程序员的世界 Copyright © 2020- www.580doc.com. Some Rights Reserved.