LeetCode笔记：183. Customers Who Never Order

Question: 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       |+-----------+

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Top Solutions:

SELECT A.Name from Customers AWHERE NOT EXISTS (SELECT 1 FROM Orders B WHERE A.Id = B.CustomerId)SELECT A.Name from Customers ALEFT JOIN Orders B on  a.Id = B.CustomerIdWHERE b.CustomerId is NULLSELECT A.Name from Customers AWHERE A.Id NOT IN (SELECT B.CustomerId from Orders B)

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My Solution:
（外层查询中WHERE需要根据Id字段寻找，不能使用Name字段，避免重名）

select Name as Customers from Customerswhere Id not in(    select Customers.Id     from Customers, Orders     where Customers.Id = Orders.CustomerId);