数据库树形结构，正反遍历

--从Root往树末梢递归
select level ,identity,pid from table_name
　　start with identity=475
　　connect by prior identity = pid

--从末梢往树ROOT递归
select level ,identity,pid,yylevel from table_name
　　start with identity=542
　　connect by prior pid = identity

oracle树形结构遍历