Oracle实现递归查询

有如下表Tree：

现在要递归查询冶炼（id=2）的所有父节点和子节点：

SELECT * FROM tree START WITH id = 2 CONNECT BY PRIOR pid = id -- 递归查询父节点
union
SELECT * FROM tree START WITH id = 2 CONNECT BY pid = PRIOR id; -- 递归查询子节点

查询结果：

当然，也可以使用in关键字递归查询多个节点的父节点和子节点：

SELECT * FROM tree START WITH id in (1, 10) CONNECT BY PRIOR pid = id -- 递归查询父节点
union
SELECT * FROM tree START WITH id in (1, 10) CONNECT BY pid = PRIOR id; -- 递归查询子节点

以上语句递归查询id为1或者10的父节点和子节点，结果如下：