2.Start with

Start with...Connect By子句递归查询一般用于一个表维护树形结构的应用。
创建示例表：
CREATE TABLE TBL_TEST
(
  ID    NUMBER,
  NAME  VARCHAR2(100 BYTE),
  PID   NUMBER                                  DEFAULT 0
);
 
插入测试数据：
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES('1','10','0');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES('2','11','1');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES('3','20','0');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES('4','12','1');
INSERT INTO TBL_TEST(ID,NAME,PID) VALUES('5','121','2');
 
从Root往树末梢递归
select * from TBL_TEST
 start with id=1
 connect by prior id = pid
 
从末梢往树ROOT递归
select * from TBL_TEST
 start with id=5
 connect by prior pid = id
资料引用:http://www.knowsky.com/390130.html

相关函数：SYS_CONNECT_BY_PATH(a,',')（用逗号连接父节点到当前行）
select SYS_CONNECT_BY_PATH(id,',') from TBL_TEST
 start with id=5
 connect by prior pid = id