查詢樹的所有葉子結點

有兩種方式，一種通用型：

SELECT a.node
  FROM tree a
 WHERE NOT existsselect (SELECT 1 FROM tree b WHERE a.node = b.parent)
 START WITH PARENT = -1 / / 一棵樹的根節點
CONNECT BY PARENT = PRIOR node;

一種使用於oracle 10g以上版本：

SELECT node
    FROM (SELECT t.node, connect_by_isleaf lf
            FROM tree t
           START WITH t.parent = -1
          CONNECT BY PRIOR t.node = t.parent)
   WHERE lf = 1

node 樹節點ID

parent 樹節點的父節點