Oracle: How to use Group by and Max(datetime) each record no duplication

Question

I want to Group by Max(Datetime) in each record, but my query has duplicate records. I don't want duplicate records.

SQL:

with temp as 
(
SELECT a.ref_period, b.status, a.updated_dtm
 FROM ir_net_cndn_detail a,ir_net_cndn b
      WHERE a.bill_no=b.bill_no
      AND b.company_code = a.company_code     
      AND TO_DATE(a.ref_period,'MM/yyyy') >= TO_DATE(&p_ref_period_start,'MM/yyyy') 
      AND TO_DATE(a.ref_period,'MM/yyyy') <= TO_DATE(&p_ref_period_end,'MM/yyyy')      
)  

   select a.ref_period, a.status, max(updated_dtm) as updated_dtm
   from temp a
   where TO_DATE(a.ref_period,'MM/yyyy') >= TO_DATE(&p_ref_period_start,'MM/yyyy') 
   AND TO_DATE(a.ref_period,'MM/yyyy') <= TO_DATE(&p_ref_period_end,'MM/yyyy')
   group by a.ref_period, a.status

Resut SQL:

ref_period |    status  | update_dtm
01/2015  |  I   | 01/09/2016 13:29:56
01/2015  |  I   | 18/05/2017 17:01:52
01/2015  |  I   | 18/05/2017 16:16:23
07/2015  |  I   | 01/09/2016 13:29:56
07/2015  |  I   | 07/01/2016 10:17:39
08/2015  |  I   | 01/09/2016 13:29:56
09/2015  |  N   | 05/06/2017 15:59:55
09/2015  |  I   | 01/09/2016 13:29:56
10/2015  |  I   | 01/09/2016 13:29:56

But I want Result:

ref_period |    status  | update_dtm  >> I want max(update)/1 record with no duplication
01/2015  |  I   | 18/05/2017 17:01:52
07/2015  |  I   | 01/09/2016 13:29:56
08/2015  |  I   | 01/09/2016 13:29:56
09/2015  |  N   | 05/06/2017 15:59:55
10/2015  |  I   | 01/09/2016 13:29:56

Answer 1

You should only group by ref_period , why are you also grouping by status ? Rather, group by ref_period , select max(update_dtm) , and - to get the status as well - use the LAST function (see the documentation if you are not familiar with it). https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions056.htm

...
select   ref_period,
         min(status) keep (dense_rank last order by update_dtm) as status,
         max(update_dtm) as update_dtm
from     temp
group by ref_period