ORA-01427 单行子查询返回多个行 解决方法
数据库分级结构中，删除叶子节点后需要将其父节点的的状态重新判断是否为叶子节点。根据ORACLE语句可直接查询出所几点是否为叶子节点，SQL语句如下：

UPDATE am_sys_entity_code t1 SET t1.s_mark_tail = (       select t2.s_mark_tail from (              SELECT s_entity_code,                NVL((SELECT '0'                  FROM am_sys_entity_code B                  WHERE I.s_entity_code=B.s_parent_code                  AND ROWNUM  < 2),'1') S_MARK_TAIL                  FROM am_sys_entity_code I                 START WITH s_parent_code = '0'                CONNECT BY s_parent_code = PRIOR s_entity_code       ) t2 where t2.s_entity_code = t1.s_entity_code);