Oracle SQL - DENSE_RANK

Question

I have a Client data table, selected columns of which are shown below:

Row_ID  Client_ID  Status_ID  From_date           To_date
  1     123456       4               


        

Answer 1

the thing is that you need to partition your ranking over the CHANGE of the status, not the VALUE of the status. I'm leaving some extra columns in the output so that you can see how it is all derived:

WITH dat as (
 SELECT 1 row_id,     123456 client_id,      4 status,       to_date('20/12/2007 18:02','dd/mm/yyyy hh24:mi') frdate,    to_date('20/12/2007 18:07','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   2 row_id,     789087  client_id,       4 status,        to_date('20/12/2007 18:02','dd/mm/yyyy hh24:mi') frdate,    to_date('20/12/2007 18:07','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   3 row_id,     789087 client_id,        4  status,       to_date('20/12/2007 18:07','dd/mm/yyyy hh24:mi') frdate,    to_date('20/12/2007 18:50','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   4 row_id,     789087 client_id,        4 status,        to_date('20/12/2007 18:50','dd/mm/yyyy hh24:mi') frdate,    to_date('21/12/2007 10:38','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   5  row_id,    123456 client_id,        4 status,        to_date('20/12/2007 18:07','dd/mm/yyyy hh24:mi') frdate,    to_date('20/12/2007 18:50','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   6 row_id,     123456 client_id,        4 status,        to_date('20/12/2007 18:50','dd/mm/yyyy hh24:mi') frdate,    to_date('21/12/2007 10:38','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   7  row_id,    123456 client_id,        4 status,        to_date('21/12/2007 10:38','dd/mm/yyyy hh24:mi') frdate,    to_date('21/12/2007 16:39','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   8 row_id,     789087  client_id,       4  status,       to_date('21/12/2007 10:38','dd/mm/yyyy hh24:mi') frdate,    to_date('21/12/2007 17:54','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT   9 row_id,     789087  client_id,       4 status,        to_date('21/12/2007 17:54','dd/mm/yyyy hh24:mi') frdate,    to_date('21/12/2007 18:32','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT  10 row_id,     789087 client_id,        4 status,        to_date('21/12/2007 18:32','dd/mm/yyyy hh24:mi') frdate,    to_date('22/12/2007 06:48','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT  11 row_id,     123456  client_id,       5 status,        to_date('21/12/2007 16:39','dd/mm/yyyy hh24:mi') frdate,    null from dual union all
 SELECT  12 row_id,     789087 client_id,        5 status,        to_date('22/12/2007 06:48','dd/mm/yyyy hh24:mi') frdate,    to_date('22/12/2007 10:53','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT  13 row_id,     789087 client_id,        4  status,       to_date('22/12/2007 10:53','dd/mm/yyyy hh24:mi') frdate,    to_date('22/12/2007 11:51','dd/mm/yyyy hh24:mi') todate from dual union all
 SELECT  14 row_id,     789087 client_id,        5 status,        to_date('22/12/2007 11:51','dd/mm/yyyy hh24:mi') frdate,    null from dual)
SELECT t1.*, DENSE_RANK () OVER (ORDER BY t1.client_id, t1.chg_status) rank_id
FROM (select client_id, status, prev_status, sum(case when nvl(prev_status,-1) != status then 1 else 0 end) over (partition by client_id order by frdate) chg_status, frdate, todate
      from (
      SELECT c.client_ID
           , c.status
           , lag(status) over (partition by client_id order by frdate) as prev_status
           , c.frdate
           , c.todate
      FROM dat c
      ORDER BY c.client_id, c.frdate)) t1
ORDER BY t1.client_id, t1.frdate

Returns:

CLIENT_ID, STATUS, PREV_STATUS, CHG_STATUS,  FRDATE,                 TODATE,              RANK_ID
123456,    4,      ,            1,           20/12/2007 6:02:00 PM, 20/12/2007 6:07:00 PM, 1
123456,    4,      4,            1,          20/12/2007 6:07:00 PM, 20/12/2007 6:50:00 PM, 1
123456,    4,      4,            1,          20/12/2007 6:50:00 PM, 21/12/2007 10:38:00 AM, 1
123456,    4,      4,            1,          21/12/2007 10:38:00 AM, 21/12/2007 4:39:00 PM, 1
123456,    5,      4,            2,          21/12/2007 4:39:00 PM,,                       2
789087,    4,      ,            1,           20/12/2007 6:02:00 PM,20/12/2007 6:07:00 PM, 3
789087,    4,      4,            1,          20/12/2007 6:07:00 PM,20/12/2007 6:50:00 PM, 3
789087,    4,      4,            1,          20/12/2007 6:50:00 PM, 21/12/2007 10:38:00 AM, 3
789087,    4,      4,            1,          21/12/2007 10:38:00 AM, 21/12/2007 5:54:00 PM, 3
789087,    4,      4,            1,          21/12/2007 5:54:00 PM, 21/12/2007 6:32:00 PM, 3
789087,    4,      4,            1,          21/12/2007 6:32:00 PM,22/12/2007 6:48:00 AM, 3
789087,    5,      4,            2,          22/12/2007 6:48:00 AM, 22/12/2007 10:53:00 AM, 4
789087,    4,      5,            3,          22/12/2007 10:53:00 AM, 22/12/2007 11:51:00 AM, 5
789087,    5,      4,            4,          22/12/2007 11:51:00 AM,,                      6