608. 树节点

608. 树节点

/* 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