Dense Rank with order by

Question

I have Assignment Table like this

EMPLID | RCD | COMPANY |   EFFDT       |  SALARY
---------------------------------------------------
100    | 0   | xyz     |   1/1/2000    |    1000
100    | 0   | xyz     |   1/15/2000   |    1100
100    | 0   | xyz     |   1/31/2000   |    1200
100    | 0   | ggg     |   2/15/2000   |    1500
100    | 1   | abc     |   3/1/2000    |    2000
100    | 1   | abc     |   4/1/2000    |    2100

I need a counter which should increase whenever RCD or Company combination changes and it should be order by effdt.

EMPLID | RCD | COMPANY |   EFFDT       |  SALARY     | COUNTER
-------|-----|---------|---------------|-------------|----------
100    | 0   | xyz     |   1/1/2000    |    1000     | 1
100    | 0   | xyz     |   1/15/2000   |    1100     | 1
100    | 0   | xyz     |   1/31/2000   |    1200     | 1
100    | 0   | ggg     |   2/15/2000   |    1500     | 2
100    | 1   | abc     |   3/1/2000    |    2000     | 3
100    | 1   | abc     |   4/1/2000    |    2100     | 3

I tried Dense_Rank function with order by EMPLID , RCD , COMPANY , It provides me Counter but its not in order by effdt.

SELECT EMPLID,RCD,COMPANY,EFFDT,
    DENSE_RANK() over (order by EMPLID , RCD , COMPANY) AS COUNTER
FROM ASSIGNMENT ;

Order by EFFDT , Gives incremental counter 1 ... 6

SELECT EMPLID,RCD,COMPANY,EFFDT,
  DENSE_RANK() over (order by EFFDT) AS COUNTER 
FROM ASSIGNMENT;

Kindly help me to find out what I am missing.

Answer 1

Try LAG

WITH flagged AS (  
    SELECT *, 
      CASE WHEN LAG(RCD) OVER(PARTITION BY EMPLID ORDER BY EFFDT) = RCD 
              AND LAG(COMPANY) OVER(PARTITION BY EMPLID ORDER BY EFFDT) = COMPANY THEN 0 ELSE 1 END strtFlag
    FROM tbl
    )

SELECT EMPLID, RCD, COMPANY, EFFDT, SALARY, SUM(strtFlag) OVER(PARTITION BY EMPLID ORDER BY EFFDT) COUNTER
FROM flagged

alternatively, with DENSE_RANK() of group

WITH grps AS (  
    SELECT *, 
      ROW_NUMBER() OVER(PARTITION BY EMPLID ORDER BY EFFDT) -
      ROW_NUMBER() OVER(PARTITION BY EMPLID, RCD, COMPANY ORDER BY EFFDT) grp
    FROM tbl
    )

SELECT EMPLID, RCD, COMPANY, EFFDT, SALARY
  , DENSE_RANK() OVER(PARTITION BY EMPLID ORDER BY grp) COUNTER
FROM grps

Anyway looks like two steps are needed to get dense numbering.

Answer 2

This should work - with the clarification that a combination of rcd and company should keep the same "counter" even if it appears in non-consecutive periods. I added to more rows to the test data to make sure I get the correct result.

Like Serg's solutions (which answer a different question), the solution does one pass over the base data, and then a second pass over the results of the first pass (all in memory, so it should be relatively fast). There's no way around that - this requires two different analytic functions where one depends on the results of the other, and nested analytic functions are not allowed. (This part of the answer addresses a comment by the OP to the Answer by Serg.)

with
     test_data ( emplid, rcd, company, effdt, salary ) as (
       select 100, 0, 'xyz', to_date('1/1/2000' , 'mm/dd/yyyy'), 1000 from dual union all
       select 100, 0, 'xyz', to_date('1/15/2000', 'mm/dd/yyyy'), 1100 from dual union all
       select 100, 0, 'xyz', to_date('1/31/2000', 'mm/dd/yyyy'), 1200 from dual union all
       select 100, 0, 'ggg', to_date('2/15/2000', 'mm/dd/yyyy'), 1500 from dual union all
       select 100, 1, 'abc', to_date('3/1/2000' , 'mm/dd/yyyy'), 2000 from dual union all
       select 100, 1, 'abc', to_date('4/1/2000' , 'mm/dd/yyyy'), 2100 from dual union all
       select 100, 0, 'xyz', to_date('5/1/2000' , 'mm/dd/yyyy'), 2200 from dual union all
       select 100, 1, 'ggg', to_date('8/15/2000', 'mm/dd/yyyy'), 2300 from dual
     )
-- end of test data; the actual solution (SQL query) begins below this line
select emplid, rcd, company, effdt, salary,
       dense_rank() over (partition by emplid order by min_dt) as counter
from ( select emplid, rcd, company, effdt, salary, 
              min(effdt) over (partition by emplid, rcd, company) as min_dt
       from   test_data )
order by effdt                --   ORDER BY is optional
;

    EMPLID        RCD COM EFFDT                   SALARY    COUNTER
---------- ---------- --- ------------------- ---------- ----------
       100          0 xyz 2000-01-01 00:00:00       1000          1
       100          0 xyz 2000-01-15 00:00:00       1100          1
       100          0 xyz 2000-01-31 00:00:00       1200          1
       100          0 ggg 2000-02-15 00:00:00       1500          2
       100          1 abc 2000-03-01 00:00:00       2000          3
       100          1 abc 2000-04-01 00:00:00       2100          3
       100          0 xyz 2000-05-01 00:00:00       2200          1
       100          1 ggg 2000-08-15 00:00:00       2300          4

 8 rows selected