Customers Who Never Order，customersorder

Customers Who Never Order，customersorder

    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       |    +-----------+    執行左外串連，然後判斷customerid is null的記錄    select name,customerid from Customers c left outer join Orders o on c.id=o.customerid    +-------+------------+    | name  | customerid |    +-------+------------+    | Joe   |          1 |    | Henry |       NULL |    | Sam   |          3 |    | Max   |       NULL |    +-------+------------+    select name as Customers from (select name,customerid from Customers c left outer join Orders o on c.id=o.customerid) t where t.customerid is null;