feat: 每日一题 2019-06-21

Author: luzhipeng

Diff for: daily/2019-06-21.md

@@ -0,0 +1,62 @@
+## 每日一题 - Nth Highest Salary
+
+### 信息卡片
+
+- 时间：2019-06-21
+- 题目链接：https://leetcode.com/problems/nth-highest-salary/
+- tag：`sql`
+
+### 题目描述
+
+```
+Write a SQL query to get the nth highest salary from the Employee table.
+
++----+--------+
+| Id | Salary |
++----+--------+
+| 1  | 100    |
+| 2  | 200    |
+| 3  | 300    |
++----+--------+
+For example, given the above Employee table, the nth highest salary where n = 2 is 200. If there is no nth highest salary, then the query should return null.
+
++------------------------+
+| getNthHighestSalary(2) |
++------------------------+
+| 200                    |
++------------------------+
+```
+
+### 参考答案
+
+这是一个简单的考察sql基本操作的题目，我们只要orderby desc一下然后limit选取指定项即可。
+
+需要注意的是sql中好像没有N-1这样的操作，
+因此需要类似这样：
+
+```
+DECLARE M INT;
+SET M=N-1;
+
+```
+
+
+参考代码：
+
+```sql
+CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
+BEGIN
+  DECLARE M INT;
+  SET M=N-1;
+  RETURN (
+      # Write your MySQL query statement below.
+      SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT M, 1
+  );
+END
+
+```
+
+### 其他优秀解答
+```
+暂无
+```

Diff for: daily/README.md

@@ -41,20 +41,26 @@ tag: `Tree`
 
 时间: 2019-06-10
 
-### [三门问题](./2019-06-13.md)
-
-tag: `Probability Theory`
-
-时间: 2019-06-13
-
 ### [重复数据排序优化](./2019-06-11.md)
 
 tag: `Sort` `Quick Sort`
 
 时间: 2019-06-11
 
+### [三门问题](./2019-06-13.md)
+
+tag: `Probability Theory`
+
+时间: 2019-06-13
+
 ### [114.flatten-binary-tree-to-linked-list](./2019-06-14.md)
 
 tag: `tree`
 
 时间: 2019-06-14
+
+### [114.flatten-binary-tree-to-linked-list](./2019-06-21.md)
+
+tag: `sql`
+
+时间: 2019-06-21