SQL & PL/SQL

Hi Every one

I'm trying to learn oracle hierarchy query and spent couples of hours but still not getting it. Suppose I have the following query:

Query

WITH

          DATA AS

                  (

                    select '100' grp, '01-JAN-2012' effective_date, '30-JUN-2012' termination_date from dual

                    union all

                    select '100' grp, '01-JUL-2012' effective_date, '05-AUG-2012' from dual

                    union all

                    select '100' grp, '06-AUG-2012' effective_date, '10-AUG-2012' from dual

                    union all

                    select '100' grp, '02-AUG-2012' effective_date, '09-AUG-2012' from dual

                    ),

        correct_data as (

         select grp,

                to_date(effective_date, 'DD-MON-YYYY','NLS_DATE_LANGUAGE=ENGLISH') effective_date,

                to_date(termination_date, 'DD-MON-YYYY','NLS_DATE_LANGUAGE=ENGLISH') termination_date

         from data

        )

   select grp, effective_date, termination_date,level

   from correct_data

   connect by     prior  termination_date =  effective_date-1

              and prior grp = grp

   start with (effective_date)

           in (select min(effective_date) from correct_data )

   order by 1, 2;

Query result

100      01-JAN-12       30-JUN-12      1

100      01-JUL-12       05-AUG-12      2

100      06-AUG-12      10-AUG-12     3

I don't understand why I'm getting this result and not getting the remaining 1 row. if someone explain this in details in simple words then I really appreciate it. Thanks in advance.

Regards

Shumail