[ START WITH condition ]CONNECT BY [ NOCYCLE ] condition

说明：
1. START WITH：告诉系统以哪个节点作为根结点开始查找并构造结果集，该节点即为返回记录中的最高节点。
2. 当分层查询中存在上下层互为父子节点的情况时，会返回ORA-01436错误。此时，需要在connect by后面加上NOCYCLE关键字。同时，可用connect_by_iscycle伪列定位出存在互为父子循环的具体节点。 connect_by_iscycle必须要跟关键字NOCYCLE结合起来使用

[例1]

创建一个部门表，这个表有三个字段，分别对应部门ID，部门名称，以及上级部门ID

   DEPID DEPNAME                                                                           UPPERDEPID----------- -------------------------------------------------------------------------------- -----------          0 General Deparment                                                                          1 Development                                                                                0          2 QA                                                                                         0          3 Server Development                                                                         1          4 Client Development                                                                         1          5 TA                                                                                         2          6 Porject QA                                                                                 2

现在我要根据“CONNECT BY”来实现树状查询结果

SQL> SELECT RPAD( ‘ ‘, 2*(LEVEL-1), ‘-‘ ) || DEPNAME "DEPNAME",CONNECT_BY_ROOT DEPNAME "ROOT",CONNECT_BY_ISLEAF "ISLEAF",LEVEL ,SYS_CONNECT_BY_PATH(DEPNAME, ‘/‘) "PATH"FROM DEPSTART WITH UPPERDEPID IS NULLCONNECT BY PRIOR DEPID = UPPERDEPID;

DEPNAME                        ROOT                    ISLEAF      LEVEL PATH------------------------------ ------------------- ---------- ---------- --------------------------------------------------------------------------------General Deparment              General Deparment            0          1 /General Deparment -Development                  General Deparment            0          2 /General Deparment/Development ---Server Development         General Deparment            1          3 /General Deparment/Development/Server Development ---Client Development         General Deparment            1          3 /General Deparment/Development/Client Development -QA                           General Deparment            0          2 /General Deparment/QA ---TA                         General Deparment            1          3 /General Deparment/QA/TA ---Porject QA                 General Deparment            1          3 /General Deparment/QA/Porject QA

说明：
1. CONNECT_BY_ROOT 返回当前节点的最顶端节点
2. CONNECT_BY_ISLEAF 判断是否为叶子节点，如果这个节点下面有子节点，则不为叶子节点
3. LEVEL 伪列表示节点深度
4. SYS_CONNECT_BY_PATH函数显示详细路径，并用“/”分隔

总结：

1.根据树形结构查子类

select * from zhfg_soar.SP_ORG_GROUP where levelpermission = 0 and validflag = 1start with  id = ‘20130718091552GRP60000001‘ connect by prior id=PARENTID 

select * from zhfg_soar.SP_ORG_GROUP where levelpermission = 0 and validflag = 1start with  id = ‘40288181455dbe1701455ee92b9d001d‘ connect by prior PARENTID=id 

2. 根据属性结构查询父类

部分转载：http://www.cnblogs.com/lettoo/archive/2010/08/03/1791239.html

Oracle “CONNECT BY”用法