Tree node

#
# Table: Tree
# +-------------+------+
# | Column Name | Type |
# +-------------+------+
# | id          | int  |
# | p_id        | int  |
# +-------------+------+
# id is the column with unique values 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 a solution to report the type of each node in the tree.
# Return the result table in any order.
# The result format is in the following example.
# Example 1:
# Input:
# Tree table:
# +----+------+
# | id | p_id |
# +----+------+
# | 1  | null |
# | 2  | 1    |
# | 3  | 1    |
# | 4  | 2    |
# | 5  | 2    |
# +----+------+
# Output:
# +----+-------+
# | id | type  |
# +----+-------+
# | 1  | Root  |
# | 2  | Inner |
# | 3  | Leaf  |
# | 4  | Leaf  |
# | 5  | Leaf  |
# +----+-------+
# Explanation:
# Node 1 is the root node because its parent node is null and it has child nodes 2 and 3.
# Node 2 is an inner node because it has parent node 1 and child node 4 and 5.
# Nodes 3, 4, and 5 are leaf nodes because they have parent nodes and they do not have child nodes.
# Example 2:
# Input:
# Tree table:
# +----+------+
# | id | p_id |
# +----+------+
# | 1  | null |
# +----+------+
# Output:
# +----+-------+
# | id | type  |
# +----+-------+
# | 1  | Root  |
# +----+-------+
# Explanation: If there is only one node on the tree, you only need to output its root attributes.
# Note: This question is the same as  3054: Binary Tree Nodes.
#

# Write your MySQL query statement below

SELECT id,
  CASE
    WHEN p_id IS NULL THEN 'Root'
    WHEN id IN (SELECT DISTINCT p_id FROM Tree WHERE p_id IS NOT NULL) THEN 'Inner'
    ELSE 'Leaf'
  END AS type
FROM Tree;