现有如下表：test2
现在要递归查询WARD（id=2）的所有父节点和子节点：
select * from test2 start with id = 2 connect by prior pid = id --递归查询父节点 union select * from test2 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 test2 start with id in (2,3) connect by prior pid = id --递归查询父节点 union select * from test2 start with id in (2,3) connect by pid = prior id --递归查询子节点
查询结果：
补注：也可以加 where 和 and限制
