update

Author: kamyu104

MySQL/combine-two-tables.sql

@@ -0,0 +1,34 @@
+# Time:  O(n), n is size of Person Table
+# Space: O(n)
+#
+# Table: Person
+#
+# +-------------+---------+
+# | Column Name | Type    |
+# +-------------+---------+
+# | PersonId    | int     |
+# | FirstName   | varchar |
+# | LastName    | varchar |
+# +-------------+---------+
+# PersonId is the primary key column for this table.
+# Table: Address
+#
+# +-------------+---------+
+# | Column Name | Type    |
+# +-------------+---------+
+# | AddressId   | int     |
+# | PersonId    | int     |
+# | City        | varchar |
+# | State       | varchar |
+# +-------------+---------+
+# AddressId is the primary key column for this table.
+#
+# Write a SQL query for a report that provides the following information for each person in the Person table, regardless if there is an address for each of those people:
+#
+#FirstName, LastName, City, State
+#
+#
+# Write your MySQL query statement below
+SELECT FirstName, LastName, City, State FROM Person LEFT JOIN Address
+       ON Person.PersonId=Address.PersonId
+

MySQL/nth-highest-salary.sql

@@ -0,0 +1,26 @@
+# Time:  O(n^2)
+# Space: O(n)
+#
+# 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.
+#
+CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
+BEGIN
+  RETURN (
+     # Write your MySQL query statement below.
+     SELECT MAX(Salary) /*This is the outer query part */
+            FROM Employee Emp1
+            WHERE (N-1) = ( /* Subquery starts here */
+                 SELECT COUNT(DISTINCT(Emp2.Salary))
+                        FROM Employee Emp2
+                        WHERE Emp2.Salary > Emp1.Salary)
+                 );
+END

MySQL/second-highest-salary.sql

@@ -0,0 +1,17 @@
+# Time:  O(n)
+# Space: O(1)
+#
+# Write a SQL query to get the second highest salary from the Employee table.
+#
+# +----+--------+
+# | Id | Salary |
+# +----+--------+
+# | 1  | 100    |
+# | 2  | 200    |
+# | 3  | 300    |
+# +----+--------+
+# For example, given the above Employee table, the second highest salary is 200. If there is no second highest salary, then the query should return null.
+#
+# Write your MySQL query statement below
+SELECT MAX(Salary) FROM Employee
+WHERE Salary NOT IN (SELECT MAX(Salary) FROM Employee)

README.md

@@ -1,12 +1,14 @@
 LeetCode
 ======== 
 
-Up to date (2015-01-06), there are total `174` problems on [LeetCode Online Judge](https://oj.leetcode.com/).
+Up to date (2015-01-12), there are total `177` problems on [LeetCode Online Judge](https://oj.leetcode.com/).
 The number of problems is increasing recently.
-Here is the classification of all `174` problems.
+Here is the classification of all `177` problems.
 I'll keep updating for full summary and better solutions. Stay tuned for updates.
 
 --- 
+Algorithm
+====
 
 * [Bit Manipulation](https://github.com/kamyu104/LeetCode#bit-manipulation)
 * [Array](https://github.com/kamyu104/LeetCode#array)
@@ -29,6 +31,12 @@ I'll keep updating for full summary and better solutions. Stay tuned for updates
 * [Backtracking](https://github.com/kamyu104/LeetCode#backtracking)
 * [Greedy](https://github.com/kamyu104/LeetCode#greedy)
 
+
+DataBase
+===
+
+* [SQL](https://github.com/kamyu104/LeetCode#sql)
+
 ---
 
 ##Bit Manipulation
@@ -698,3 +706,18 @@ Problem         |  Solution       |  Time           | Space           | Difficul
 [trapping-rain-water.py]:https://github.com/kamyu104/LeetCode/blob/master/Python/trapping-rain-water.py
 [Wildcard Matching]:https://oj.leetcode.com/problems/wildcard-matching/
 [wildcard-matching.py]:https://github.com/kamyu104/LeetCode/blob/master/Python/wildcard-matching.py
+
+##SQL
+Problem         |  Solution       |  Time           | Space           | Difficulty     | Notes
+--------------- | --------------- | --------------- | --------------- | -------------- | -----
+[Combine Two Tables] | [combine-two-tables.sql] | _O(m + n)_   | _O(m + n)_ | Easy     |
+[Nth Highest Salary] | [nth-highest-salary.sql] | _O(n^2)_   | _O(n)_ | Medium         |
+[Second Highest Salary] | [second-highest-salary.sql] | _O(n)_ | _O(1)_ | Easy         |
+
+[Combine Two Tables]:https://oj.leetcode.com/problems/combine-two-tables/
+[combine-two-tables.sql]:https://github.com/kamyu104/LeetCode/blob/master/MySQL/combine-two-tables.sql
+[Nth Highest Salary]:https://oj.leetcode.com/problems/nth-highest-salary/
+[nth-highest-salary.sql]:https://github.com/kamyu104/LeetCode/blob/master/MySQL/nth-highest-salary.sql
+[Second Highest Salary]:https://oj.leetcode.com/problems/second-highest-salary/
+[second-highest-salary.sql]:https://github.com/kamyu104/LeetCode/blob/master/MySQL/second-highest-salary.sql
+