add 608

Author: fishercoder1534

README.md

@@ -599,6 +599,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |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 | 
+|608|[Tree Node](https://leetcode.com/problems/tree-node/)|[Solution](../master/database/_608.sql) | | | Medium | Union
 |607|[Sales Person](https://leetcode.com/problems/sales-person/)|[Solution](../master/database/_607.sql) | | | Easy |
 |602|[Friend Requests II: Who Has the Most Friends](https://leetcode.com/problems/friend-requests-ii-who-has-the-most-friends/)|[Solution](../master/database/_602.sql) | | | Medium |
 |597|[Friend Requests I: Overall Acceptance Rate](https://leetcode.com/problems/friend-requests-i-overall-acceptance-rate/)|[Solution](../master/database/_597.sql) | | | Easy |

database/_608.sql

@@ -0,0 +1,55 @@
+--608. Tree Node
+--Given a table tree, id is identifier of the tree node and p_id is its parent node's id.
+--
+--+----+------+
+--| id | p_id |
+--+----+------+
+--| 1  | null |
+--| 2  | 1    |
+--| 3  | 1    |
+--| 4  | 2    |
+--| 5  | 2    |
+--+----+------+
+--Each node in the tree can be one of three types:
+--Leaf: if the node is a leaf node.
+--Root: if the node is the root of the tree.
+--Inner: If the node is neither a leaf node nor a root node.
+--Write a query to print the node id and the type of the node. Sort your output by the node id. The result for the above sample is:
+--+----+------+
+--| id | Type |
+--+----+------+
+--| 1  | Root |
+--| 2  | Inner|
+--| 3  | Leaf |
+--| 4  | Leaf |
+--| 5  | Leaf |
+--+----+------+
+--Explanation
+--
+--Node '1' is root node, because its parent node is NULL and it has child node '2' and '3'.
+--Node '2' is inner node, because it has parent node '1' and child node '4' and '5'.
+--Node '3', '4' and '5' is Leaf node, because they have parent node and they don't have child node.
+--
+--And here is the image of the sample tree as below:
+--			  1
+--			/   \
+--                      2       3
+--                    /   \
+--                  4       5
+--Note
+--
+--If there is only one node on the tree, you only need to output its root attributes.
+
+--credit: https://leetcode.com/articles/tree-node/#approach-i-using-union-accepted
+select id, 'Root' as Type from tree where p_id is null
+union
+select id, 'Leaf' as Type from tree where id not in
+    (select distinct p_id from tree
+        where p_id is not null)
+    and p_id is not null
+union
+select id, 'Inner' as Type from tree where id in
+    (select distinct p_id from tree
+        where p_id is not null)
+    and p_id is not null
+order by id;