[Leetcode] [Database] Customers Who Never Order解題

題目如下

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

題目意思: 選出沒有訂單的用戶

---

解題思路: 選出不在order中存在的用戶

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