/* Write your T-SQL query statement below */
SELECT id ,
(CASE WHEN p_id IS NULL THEN 'Root' ELSE -- 根节点，p_id为null
CASE WHEN id IN (SELECT p_id FROM tree) THEN 'Inner' ELSE 'Leaf' END -- 是否有孩子节点，若有，则内部节点，否则叶子节点
END ) AS type
FROM tree
ORDER BY id
标签：CASE,WHEN,608,节点,id,SELECT From： https://www.cnblogs.com/luyj00436/p/17096541.html