add 614

Author: fishercoder1534

README.md

@@ -596,6 +596,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |627|[Swap Salary](https://leetcode.com/problems/swap-salary/)|[Solution](../master/database/_627.sql) | | | Easy |
 |620|[Not Boring Movies](https://leetcode.com/problems/not-boring-movies/)|[Solution](../master/database/_620.sql) | | | Easy |
 |619|[Biggest Single Number](https://leetcode.com/problems/biggest-single-number/)|[Solution](../master/database/_619.sql) | | | Easy |
+|614|[Second Degree Follower](https://leetcode.com/problems/second-degree-follower/)|[Solution](../master/database/_614.sql) | | | Medium | Inner Join
 |613|[Shortest Distance in a Line](https://leetcode.com/problems/shortest-distance-in-a-line/)|[Solution](../master/database/_613.sql) | || Easy|
 |612|[Shortest Distance in a Plane](https://leetcode.com/problems/shortest-distance-in-a-plane/)|[Solution](../master/database/_612.sql) | || Medium|
 |610|[Triangle Judgement](https://leetcode.com/problems/triangle-judgement/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_610.java) | | | Easy | 

database/_614.sql

@@ -0,0 +1,32 @@
+--614. Second Degree Follower
+--In facebook, there is a follow table with two columns: followee, follower.
+--
+--Please write a sql query to get the amount of each follower’s follower if he/she has one.
+--
+--For example:
+--
+--+-------------+------------+
+--| followee    | follower   |
+--+-------------+------------+
+--|     A       |     B      |
+--|     B       |     C      |
+--|     B       |     D      |
+--|     D       |     E      |
+--+-------------+------------+
+--should output:
+--+-------------+------------+
+--| follower    | num        |
+--+-------------+------------+
+--|     B       |  2         |
+--|     D       |  1         |
+--+-------------+------------+
+--Explaination:
+--Both B and D exist in the follower list, when as a followee, B's follower is C and D, and D's follower is E. A does not exist in follower list.
+--Note:
+--Followee would not follow himself/herself in all cases.
+--Please display the result in follower's alphabet order.
+
+select f1.follower, count(distinct f2.follower) as num
+from follow f1
+inner join follow f2 on f1.follower = f2.followee
+group by f1.follower