oracle 递归查询求出起点、终点问题的解决方法

有表如下：

SQL> select * from yu1;

COL1 COL2

---------- --------------------

2014 00000001

2014 00000002

2014 00000003

2014 00000004

2014 00000005

2014 00000009

2014 00000010

2013 00000013

2013 00000014

2013 00000015

2013 00000017

COL1 COL2

---------- --------------------

2013 00000018

2013 00000020

2013 00000021

欲求出下列结果

col1 start end

2014 00000001 00000005

2014 00000009 00000010

2013 00000013 00000015

2013 00000017 00000018

2013 00000020 00000021

select col1, min(col2) "start" , max(col2) "end"
from yu1 a
start with not exists (select 1 from yu1 b where b.col2 = a.col2 - 1)
connect by prior a.col2 = a.col2 - 1
group by rownum - level, col1;