1.对于表中行与行存在父子关系时,可以通过connect by查询方式,查询行与行之间的父子关系 ),'-')|| empno as tempno, ename,mgr,level, decode(,) as root, decode(connect_by_isleaf,,) as leafnode from emp start connect by (prior empno) = mgr order by level; 除了level伪列外,connect_by_isleaf也是伪列,1表示没