1、select id from tablename start with id='idNum' connect by PRior id = parentId;- -自頂向下查詢2、select id from tablename start with id='idNum' connect by  id = prior parentId;- -自底向上查詢
1、prior在等號左邊，自頂向下查詢。prior在等號右邊自底向上查詢。
2、根據prior后面的列（id/parentId）判斷查找的是父節點還是子節點,如果為id,則查詢子節點，若為parentId則查詢父節點。