LeetCode608. Tree Node

Table: Tree

+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| p_id        | int  |
+-------------+------+
id is the primary key column for this table.
Each row of this table contains information about the id of a node and the id of its parent node in a tree.
The given structure is always a valid tree.

 

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 an SQL query to report the type of each node in the tree.

Return the result table in any order.

The query result format is in the following example.

/* Write your PL/SQL query statement below */

select id,'Root' as type from tree t where p_id is null

union

select id,'Inner' as type from tree t1 where exists(select 1 from tree where p_id = t1.id ) and p_id is not null

union

select id,'Leaf' as type from tree t2 where not exists(select 1 from tree where p_id = t2.id ) and p_id is not null