How can I return results based on 2 columns?

I have had a problem and it cannot know for life. First of all, here is a series of example data that I use so you can see exactly what I'm asking.

EmplId Effdt Effseq            

10001 1 JANUARY 99 ' 0

10001 1 JULY 11 ' 0

10001 1 JULY 11 ' 1

10001 1 JULY 11 ' 2

10001 1 JULY 12 ' 3

Do I have to do here is get 3 ranks. 3 rows, I need are lines 1, 4 and 5. I need rank 1 because it's a different date. I need line 5 for the same reason: it is another date. The question arises with how I can get the rank 4. The problem is that the lines 2, 3, 4, and all have the same date (effdt) effective, Developer SQL just returned one of these lines. Because these 3 rows all have the same date (effdt) effective the switch becomes the actual sequence number (effseq). When the date (effdt) effective is the same, you enter the maximum number of sequence (effseq) effective and return results of this whole line as the emplid, effdt and effseq. It seems so simple and something that you can use a subquery for, but its not as simple as that. Note, that you can specifically use the emplid = 10001 in any specific form because there are many employee also id, the lines will not be in a specific order so that you can always just grasp the lines 1, 4 and 5. Some employees may have only a single line in the database, and some may have 50 lines. Everything depends only on the combination of employee id (emplid) date (effdt) efficient and effective sequence (effseq) as the tiebreaker. Any help to fix this would be greatly appreciated. Thank you in advance.

WITH t
     AS (SELECT 10001 emplid,
                TO_DATE ('01-JAN-1999', 'dd-mon-yy') effdt,
                0 effseq
           FROM DUAL
         UNION ALL
         SELECT 10001, TO_DATE ('01-JUL-2011', 'dd-mon-yy'), 0 FROM DUAL
         UNION ALL
         SELECT 10001, TO_DATE ('01-JUL-2011', 'dd-mon-yy'), 1 FROM DUAL
         UNION ALL
         SELECT 10001, TO_DATE ('01-JUL-2011', 'dd-mon-yy'), 2 FROM DUAL
         UNION ALL
         SELECT 10001, TO_DATE ('01-JUL-2012', 'dd-mon-yy'), 3 FROM DUAL)
SELECT emplid, effdt, effseq
  FROM (SELECT t.*,
               ROW_NUMBER ()
                  OVER (PARTITION BY emplid, effdt ORDER BY effseq DESC)
                  rn
          FROM t)
 WHERE rn = 1
EMPLID EFFDT EFFSEQ
10001
 01/01/1999
0
10001
 01/07/2011
2
10001
 01/07/2012
3

Tags: Database

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