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 | +-----------+
解决方案如下：
select name as Customers from Customers a left join Orders b on a.Id=b.CustomerId where CustomerId is null
【leetcode SQL】Customers Who Never Order
原文：http://blog.csdn.net/exceptional_derek/article/details/43376431