Add solution 183 [sql]

left join

Author: yanglbme

README.md

@@ -38,6 +38,7 @@ Complete [solutions](https://github.com/doocs/leetcode/tree/master/solution) to
 | 176 | [Second Highest Salary](https://github.com/doocs/leetcode/tree/master/solution/176.Second%20Highest%20Salary) | `SQL` |
 | 181 | [Employees Earning More Than Their Managers](https://github.com/doocs/leetcode/tree/master/solution/181.Employees%20Earning%20More%20Than%20Their%20Managers) | `SQL` |
 | 182 | [Duplicate Emails](https://github.com/doocs/leetcode/tree/master/solution/182.Duplicate%20Emails) | `SQL` |
+| 183 | [Customers Who Never Order](https://github.com/doocs/leetcode/tree/master/solution/183.Customers%20Who%20Never%20Order) | `SQL` |
 | 189 | [Rotate Array](https://github.com/doocs/leetcode/tree/master/solution/189.Rotate%20Array) | `Array` |
 | 198 | [House Robber](https://github.com/doocs/leetcode/tree/master/solution/198.House%20Robber) | `Dynamic Programming` |
 | 203 | [Remove Linked List Elements](https://github.com/doocs/leetcode/tree/master/solution/203.Remove%20Linked%20List%20Elements) | `Linked List` |

solution/183.Customers Who Never Order/README.md

@@ -0,0 +1,59 @@
+## 从不订购的客户
+### 题目描述
+
+某网站包含两个表，`Customers` 表和 `Orders` 表。编写一个 SQL 查询，找出所有从不订购任何东西的客户。
+
+`Customers` 表：
+```
++----+-------+
+| Id | Name  |
++----+-------+
+| 1  | Joe   |
+| 2  | Henry |
+| 3  | Sam   |
+| 4  | Max   |
++----+-------+
+```
+
+`Orders` 表：
+```
++----+------------+
+| Id | CustomerId |
++----+------------+
+| 1  | 3          |
+| 2  | 1          |
++----+------------+
+```
+
+例如给定上述表格，你的查询应返回：
+```
++-----------+
+| Customers |
++-----------+
+| Henry     |
+| Max       |
++-----------+
+```
+
+### 解法
+两个表左连接，找出 `CustomerId` 为 `null` 的记录即可。
+
+```sql
+# Write your MySQL query statement below
+
+select Name as Customers 
+from Customers c
+left join Orders o
+on c.Id = o.CustomerId
+where o.CustomerId is null
+```
+
+#### Input
+```json
+{"headers": {"Customers": ["Id", "Name"], "Orders": ["Id", "CustomerId"]}, "rows": {"Customers": [[1, "Joe"], [2, "Henry"], [3, "Sam"], [4, "Max"]], "Orders": [[1, 3], [2, 1]]}}
+```
+
+#### Output
+```json
+{"headers":["Customers"],"values":[["Henry"],["Max"]]}
+```