Leetcode 183 Customers Who Never Order

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       |

+-----------+

select a.Name from Customers a

where a.Id not in (select b.CustomerId from Orders b)

或者左联后获取其中CustomerId为NULL的

select a.Name from Customers a

left join Orders b on a.Id = b.CustomerId

where b.CustomerId is NULL