add 569

Author: fishercoder1534

README.md

@@ -642,6 +642,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |577|[Employee Bonus](https://leetcode.com/problems/employee-bonus/)|[Solution](../master/database/_577.sql) | || Easy |
 |574|[Winning Candidate](https://leetcode.com/problems/winning-candidate/)|[Solution](../master/database/_574.sql) | || Medium |
 |570|[Managers with at Least 5 Direct Reports](https://leetcode.com/problems/managers-with-at-least-5-direct-reports/)|[Solution](../master/database/_570.sql) | || Medium |
+|569|[Median Employee Salary](https://leetcode.com/problems/median-employee-salary/)|[Solution](../master/database/_569.sql) | || Hard |
 |262|[Trips and Users](https://leetcode.com/problems/trips-and-users/)|[Solution](../master/database/_262.sql)||| Hard| Inner Join
 |197|[Rising Temperature](https://leetcode.com/problems/rising-temperature/)|[Solution](../master/database/_197.sql)| O(n^2)|O(n) | Easy|
 |196|[Delete Duplicate Emails](https://leetcode.com/problems/delete-duplicate-emails/)|[Solution](../master/database/_196.sql)| O(n^2)|O(n) | Easy|

database/_569.sql

@@ -0,0 +1,48 @@
+--569. Median Employee Salary
+-- The Employee table holds all employees. The employee table has three columns: Employee Id, Company Name, and Salary.
+--
+--+-----+------------+--------+
+--|Id   | Company    | Salary |
+--+-----+------------+--------+
+--|1    | A          | 2341   |
+--|2    | A          | 341    |
+--|3    | A          | 15     |
+--|4    | A          | 15314  |
+--|5    | A          | 451    |
+--|6    | A          | 513    |
+--|7    | B          | 15     |
+--|8    | B          | 13     |
+--|9    | B          | 1154   |
+--|10   | B          | 1345   |
+--|11   | B          | 1221   |
+--|12   | B          | 234    |
+--|13   | C          | 2345   |
+--|14   | C          | 2645   |
+--|15   | C          | 2645   |
+--|16   | C          | 2652   |
+--|17   | C          | 65     |
+--+-----+------------+--------+
+--
+--Write a SQL query to find the median salary of each company. Bonus points if you can solve it without using any built-in SQL functions.
+--
+--+-----+------------+--------+
+--|Id   | Company    | Salary |
+--+-----+------------+--------+
+--|5    | A          | 451    |
+--|6    | A          | 513    |
+--|12   | B          | 234    |
+--|9    | B          | 1154   |
+--|14   | C          | 2645   |
+--+-----+------------+--------+
+
+select Id, Company, Salary from
+(
+select e.Id, e.Salary, e.Company,  if( @prev = e.Company , @Rank := @Rank + 1, @Rank := 1) as rank, @prev := e.Company
+from Employee e , (select @Rank := 0, @prev := 0) as temp order by e.Company, e.Salary, e.Id
+) Ranking
+INNER JOIN
+(
+select count(*) as totalcount, Company as name from Employee e2 group by e2.Company
+) companycount
+on companycount.name = Ranking.Company
+where Rank = floor((totalcount+1)/2) or Rank = floor((totalcount+2)/2)