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(hào)左邊，自頂向下查詢。prior在等號(hào)右邊自底向上查詢。
2、根據(jù)prior后面的列（id/parentId）判斷查找的是父節(jié)點(diǎn)還是子節(jié)點(diǎn),如果為id,則查詢子節(jié)點(diǎn)，若為parentId則查詢父節(jié)點(diǎn)。