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 |
+-----------+
直接使用exists语句查询
select c.Name as Customers
from Customers as c
where not exists (select o.Id from Orders as o where c.Id = o.CustomerId);exists语句后面接一个select子查询，但实际并不返回任何数据，只返回是否有数据，存在返回true，否则false.