【力扣日記】【MySQL】183 從不訂購的客戶

某網站包含兩個表，Customers 表和 Orders 表。編寫一個 SQL 查詢，找出所有從不訂購任何東西的客戶。

Customers 表：
+----+-------+
| Id | Name  |
+----+-------+
| 1  | Joe   |
| 2  | Henry |
| 3  | Sam   |
| 4  | Max   |
+----+-------+
Orders 表：
+----+------------+
| Id | CustomerId |
+----+------------+
| 1  | 3          |
| 2  | 1          |
+----+------------+

即是查找ID不在orders表中的客戶名。

語句

子查詢+IN

select name Customers from Customers where id not in (select CustomerId from Orders)

左查詢

select c.Name as Customers from Customers c left join Orders o on o.CustomerId = c.Id where o.Id is null;

EXISTS

select c.Name as Customers from Customers c where not exists (select 1 from Orders o where o.CustomerId = c.Id);