[HackerRank SQL] Binary Tree Nodes

문제 link
https://www.hackerrank.com/challenges/binary-search-tree-1/problem

Code link
https://github.com/JamesJung01/Hackerrank_sql/blob/main/02_Medium/Binary_Tree_Nodes.sql

SELECT CASE
    WHEN P IS NULL THEN CONCAT(N, ' Root')
    WHEN N IN (SELECT DISTINCT P FROM BST) THEN CONCAT(N, ' Inner')
    ELSE CONCAT(N, ' Leaf')
    END
FROM BST
ORDER BY N;