Date Range Calculations for gaps and overlaps

Question

Oracle version: 11.2.0.3
Platform : Linux
Empno       position    start_dt       end_dt
     1                X            01/01/2008  01/02/2010
     1                Y           01/02/2009  12/31/2012
     1                X           02/01/2012   04/01/2013    
     1                Z           5/01/2012    12/31/2012
     1                Y           05/01/2013  present         
I need to find the exact time period the employee worked for the company in a particular position. The query should be able to calculate the overlap/gaps accordingly
For example in this case the result should be
Empno  position   days    Total_Days
1             x              1156        2943
1             y              1543        2943
1             z               244        2943
Thanks
Kevin

Answer 1

Hi, Kevin,
Assuming you do have overlaps (and depending on what you mean by "overlaps") here's one way to handle them:
WITH got_new_grp AS
   SELECT  empno, position, start_dt
   ,       NVL (end_dt, TRUNC (SYSDATE)) AS end_dt
   ,       CASE
               WHEN  MAX (end_dt)
                         OVER ( PARTITION BY  empno, position
                                ORDER BY      start_dt
                                ROWS BETWEEN  UNBOUNDED PRECEDING
                                     AND      1         PRECEDING
                              ) < start_dt
               THEN  1
               ELSE  0
           END  AS new_grp
    FROM   table_x
--  WHERE  ... -- If you need any filtering, put it here
, got_grp  AS
    SELECT  empno, position, start_dt, end_dt
    ,       SUM (new_grp) OVER ( PARTITION BY  empno, position
                                 ORDER BY      start_dt
                               )  AS grp
    FROM    got_new_grp
SELECT DISTINCT
          empno, position
,         SUM (MAX (end_dt) - MIN (start_dt))
              OVER (PARTITION BY empno, position)   AS days
,         SUM (MAX (end_dt) - MIN (start_dt))
              OVER (PARTITION BY empno)             AS total_days
FROM      got_grp
GROUP BY  empno, position, grp
ORDER BY  position
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) for all tables involved, and also post the results you want from that data.
Point out where the statement above is getting the wrong results, and explain, using specific examples, how you get the right results from the given data in those places.
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