SQL Help getting Max() date....

Question

Hi gurus, Here is my situation:
Here is the sample data:
Policy_Id Policy-Exp_Dt COl_1
123_____10/30/2008 __ 333
123_____ 09/25/2008___445
123_____ 08/30/2008___443
Here i have to get the Policy-Exp_Dt from the second row; In other words for all rows which have a similar Policy_Id i should first find out the max(Policy-Exp_Dt) and get the next smallest available date to that.
I have tried using
select Policy_Id, COl_1, Policy_Exp_Dt from
table_1
where Policy-Exp_Dt = (select max(Policy-Exp_Dt)-1 from
table_1 a
where a.policy_id = table_1.policy_id)
but here i am getting the value = 10/30/2008 - 1 which is 10/29/2008 but i need the value 9/25/2008 which is the next available date less than the max() date.
Please Advise.
Edited by: user521009 on Jan 9, 2009 1:56 PM

Answer 1

I thought to use lag - maybe not as appropriate a ranking functions.
Also we have a case where there is only One record for a policy - exclude this I guess!
drop table Max_but_One;
create table Max_but_One
  Policy_Id      integer      not null,
  Policy_Expires date         not null,
  Policy_Note    varchar2(20) not null
-- Standard data
insert into Max_but_One values (123, to_date('30-08-2008','dd-mm-yyyy'), 'First note');
insert into Max_but_One values (123, to_date('25-09-2008','dd-mm-yyyy'), 'Second note');
insert into Max_but_One values (123, to_date('30-10-2008','dd-mm-yyyy'), 'Third note');
-- Standard data again for double check
insert into Max_but_One values (223, to_date('01-11-2008','dd-mm-yyyy'), 'First note');
insert into Max_but_One values (223, to_date('02-11-2008','dd-mm-yyyy'), 'Second note');
-- Only one record for a policy!
insert into Max_but_One values (323, to_date('01-12-2008','dd-mm-yyyy'), 'First note');
-- Two or more records for a policy both having the same date which is prior to the max
insert into Max_but_One values (423, to_date('10-12-2008','dd-mm-yyyy'), 'First note');
insert into Max_but_One values (423, to_date('10-12-2008','dd-mm-yyyy'), 'Second note');
insert into Max_but_One values (423, to_date('11-12-2008','dd-mm-yyyy'), 'Third note');
break on Policy_ID
select Policy_Id, Policy_Expires, Policy_Note
  from Max_but_One
order by Policy_Id, Policy_Expires
POLICY_ID POLICY_EX POLICY_NOTE
       123 30-AUG-08 First note
           25-SEP-08 Second note
           30-OCT-08 Third note
       223 01-NOV-08 First note
           02-NOV-08 Second note
       323 01-DEC-08 First note
       423 10-DEC-08 First note
           10-DEC-08 Second note
           11-DEC-08 Third note
-- Max Policy_Expires
select t.*
  from (select Policy_Id, Policy_Expires, Policy_Note
              ,max(Policy_Expires) over (partition by Policy_Id) as Max_Policy_Expires
          from Max_but_One
       ) t
where t.Policy_Expires = t.Max_Policy_Expires
POLICY_ID POLICY_EX POLICY_NOTE          MAX_POLIC
       123 30-OCT-08 Third note           30-OCT-08
       223 02-NOV-08 Second note          02-NOV-08
       323 01-DEC-08 First note           01-DEC-08
       423 11-DEC-08 Third note           11-DEC-08
-- Using LAG
select t.Policy_Id
      ,t.Prior_Policy_Expires as Policy_Expires
      ,t.Prior_Policy_Note    as Policy_Note
  from (select Policy_Id, Policy_Expires, Policy_Note
              ,max(Policy_Expires) over (partition by Policy_Id) as Max_Policy_Expires
            ,lag(Policy_Expires) over (partition by Policy_Id order by Policy_Expires) as Prior_Policy_Expires
              ,lag(Policy_Note)    over (partition by Policy_Id order by Policy_Expires) as Prior_Policy_Note
          from Max_but_One
       ) t
where t.Policy_Expires = t.Max_Policy_Expires
POLICY_ID POLICY_EX POLICY_NOTE
       123 25-SEP-08 Second note
       223 01-NOV-08 First note
       323
       423 10-DEC-08 Second note
-- To exclude the single record policy then add and t.Prior_Policy_Expires is not null
select t.Policy_Id
      ,t.Prior_Policy_Expires as Policy_Expires
      ,t.Prior_Policy_Note    as Policy_Note
  from (select Policy_Id, Policy_Expires, Policy_Note
              ,max(Policy_Expires) over (partition by Policy_Id) as Max_Policy_Expires
            ,lag(Policy_Expires) over (partition by Policy_Id order by Policy_Expires) as Prior_Policy_Expires
              ,lag(Policy_Note)    over (partition by Policy_Id order by Policy_Expires) as Prior_Policy_Note
          from Max_but_One
       ) t
where t.Policy_Expires = t.Max_Policy_Expires
   and t.Prior_Policy_Expires is not null
POLICY_ID POLICY_EX POLICY_NOTE
       123 25-SEP-08 Second note
       223 01-NOV-08 First note
       423 10-DEC-08 Second note
-- 423 is randomly picked here - could equally have got {423, 10-DEC-08, First note}