Trying to get ending effective date for groups of rows

Question

Hi Everyone,
I've searched the forums, but I can't find a post that presents a problem quite like this.
I have some data that looks like this:
        ID_NUM     EFFECTIVE ALLOC_PERCENT   ACCT
       101 01-JUL-11            21   A1
       101 01-JUL-11            72   A2
       101 01-JUL-11             7   A3
       101 01-JUL-12            20   B1
       101 01-JUL-12            80   B2
       101 01-JAN-13            20   A1
       101 01-JAN-13            20   A2
       101 01-JAN-13            50   A3
       101 01-JAN-13            10   B1
       101 01-JUN-13            50   A1
       101 01-JUN-13            50   A2(note - I manually inserted blank lines for clarity)
Here's the logic: The rows represent a percentage allocation to the account number for the specified id number, for that effective date. A newer effective date supercedes previous ones, and if any row in the conceptual group is superceded, then they all are.
I'm trying to find out the date when each group's effective period ended, and include that in the result set so that I can subsequently calculate the number of days a given row was effective; something like this;
  ID_NUM     EFFECTIVE END_DATE   ALLOC_PERCENT ACCT
       101 01-JUL-11 01-JUL-12             21 A1
       101 01-JUL-11 01-JUL-12             72 A2
       101 01-JUL-11 01-JUL-12              7 A3
       101 01-JUL-12 01-JAN-13             20 B1
       101 01-JUL-12 01-JAN-13             80 B2
       101 01-JAN-13 01-JUN-13             20 A1
       101 01-JAN-13 01-JUN-13             20 A2
       101 01-JAN-13 01-JUN-13             50 A3
       101 01-JAN-13 01-JUN-13             10 B1
       101 01-JUN-13 <null>                50 A1
       101 01-JUN-13 <null>                50 A2The END_DATE of the group is the EFFECTIVE_DATE of the following group (ordered by ID_NUM, EFFECTIVE_DATE).
The last two rows' END_DATE is null because there is no group of rows with a later effective date - in my process, I'll NVL that to sysdate so that my days calculations will be valid.
I tried some analytic queries with LEAD, but I couldn't figure out how to make it get the next group's effective date. I could get the next row's effective date, but not the next group's. I couldn't specify how many lead rows to look ahead, because there is not a consistent number of rows in each group.
How do I populate the END_Date column?
Here's the code to create the above.
create table t
(id_num number,
effective_date date,
alloc_percent number,
acct_code varchar2(4)
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jul-2011',21.0,'A1');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jul-2011',72.0,'A2');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jul-2011',7.0,'A3');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jul-2012',20.0,'B1');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jul-2012',80.0,'B2');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jan-2013',20.0,'A1');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jan-2013',20.0,'A2');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jan-2013',50.0,'A3');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jan-2013',10.0,'B1');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jun-2013',50.0,'A1');
insert into t (id_num,Effective_date,alloc_percent,acct_code) values(101,'01-jun-2013',50.0,'A2');
commit;
select * from t;Oracle version information:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
"CORE     11.2.0.3.0     Production"
TNS for Solaris: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
Thank you very much

Answer 1

select  id_num,
        effective_date,
        first_value(effective_date)
          over(
               partition by id_num
               order by effective_date
               range between 1 following and unbounded following
              ) end_date,
        alloc_percent,
        acct_code
  from  t
  order by id_num,
           effective_date
    ID_NUM EFFECTIVE END_DATE  ALLOC_PERCENT ACCT
       101 01-JUL-11 01-JUL-12            21 A1
       101 01-JUL-11 01-JUL-12            72 A2
       101 01-JUL-11 01-JUL-12             7 A3
       101 01-JUL-12 01-JAN-13            20 B1
       101 01-JUL-12 01-JAN-13            80 B2
       101 01-JAN-13 01-JUN-13            20 A1
       101 01-JAN-13 01-JUN-13            10 B1
       101 01-JAN-13 01-JUN-13            20 A2
       101 01-JAN-13 01-JUN-13            50 A3
       101 01-JUN-13                      50 A1
       101 01-JUN-13                      50 A2
11 rows selected.
SQL> SY.