Add solution 177 [sql]

Author: yanglbme

README.md

@@ -87,6 +87,7 @@ Complete [solutions](https://github.com/doocs/leetcode/tree/master/solution) to
 | 144 | [Binary Tree Preorder Traversal](https://github.com/doocs/leetcode/tree/master/solution/144.Binary%20Tree%20Preorder%20Traversal) | `Stack`, `Tree` |
 | 150 | [Evaluate Reverse Polish Notation](https://github.com/doocs/leetcode/tree/master/solution/150.Evaluate%20Reverse%20Polish%20Notation) | `Stack` |
 | 153 | [Find Minimum in Rotated Sorted Array](https://github.com/doocs/leetcode/tree/master/solution/153.Find%20Minimum%20in%20Rotated%20Sorted%20Array) | `Array`, `Binary Search` |
+| 177 | [Nth Highest Salary](https://github.com/doocs/leetcode/tree/master/solution/177.Nth%20Highest%20Salary) | `SQL` |
 | 328 | [Odd Even Linked List](https://github.com/doocs/leetcode/tree/master/solution/328.Odd%20Even%20Linked%20List) | `Linked List` |
 
 

solution/177.Nth Highest Salary/README.md

@@ -0,0 +1,80 @@
+## 第N高的薪水
+### 题目描述
+
+编写一个 SQL 查询，获取 `Employee` 表中第 n 高的薪水（Salary）。
+```
++----+--------+
+| Id | Salary |
++----+--------+
+| 1  | 100    |
+| 2  | 200    |
+| 3  | 300    |
++----+--------+
+```
+
+例如上述 `Employee` 表，n = 2 时，应返回第二高的薪水 `200`。如果不存在第 n 高的薪水，那么查询应返回 null。
+```
++------------------------+
+| getNthHighestSalary(2) |
++------------------------+
+| 200                    |
++------------------------+
+```
+
+### 解法
+对 Salary 进行分组，然后根据 Salary 降序排列。选出偏移为 n-1 的一个记录即可。
+
+```sql
+CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
+BEGIN
+  SET N = N - 1;
+  RETURN (
+      # Write your MySQL query statement below.
+      select Salary from Employee group by Salary order by Salary desc limit 1 offset N
+  );
+END
+
+```
+
+#### Input
+```json
+{
+    "headers": {
+        "Employee": [
+            "Id",
+            "Salary"
+        ]
+    },
+    "argument": 2,
+    "rows": {
+        "Employee": [
+            [
+                1,
+                100
+            ],
+            [
+                2,
+                200
+            ],
+            [
+                3,
+                300
+            ]
+        ]
+    }
+}
+```
+
+#### Output
+```json
+{
+    "headers": [
+        "getNthHighestSalary(2)"
+    ],
+    "values": [
+        [
+            200
+        ]
+    ]
+}
+```