oracle connect by 和start with

网上找了个例子 测试了一下 貌似明白了
create table t2(
root_id number,
id number,
name varchar(5),
description varchar(10)
);

insert into t2(root_id,id,name,description) values(0,1,'a','aaa');
insert into t2(root_id,id,name,description) values(1,2,'a1','aaa1');
insert into t2(root_id,id,name,description) values(1,3,'a2','aaa2');
insert into t2(root_id,id,name,description) values(0,4,'b','bbb');
insert into t2(root_id,id,name,description) values(4,5,'b1','bbb1');
insert into t2(root_id,id,name,description) values(4,6,'b2','bbb2');

 

select * from t2 start with root_id = 0 connect by prior id = root_id
 

select * from t2 start with id = 1 connect by prior id = root_id;
 


select * from t2 start with id = 4 connect by prior id = root_id;
 

select * from t2 start with root_id = 0 connect by id = root_id;

 
select * from t2 start with id = 1 connect by id = root_id;