[리트코드/SQL] 13. Tree node (608)

👉https://leetcode.com/problems/tree-node/description/?envType=study-plan&id=sql-i

Tree Node - LeetCode

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🤔 문제 분석

1) Write an SQL query to report the type of each node in the 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.

2) Return the result table in any order.

 

 

💡 풀이

SELECT
    distinct t1.id,
     CASE
        WHEN t1.p_id IS NULL THEN "Root"
        WHEN t2.id IS NOT NULL THEN "Inner"
        ELSE "Leaf" 
    END AS "type"
FROM Tree AS t1
    LEFT JOIN Tree AS t2 ON t1.id = t2.p_id