Combining consecutive date ranges

Question

Using SQL Server 2008 R2,

I am trying to combine date ranges into a maximum date range given that one end date is next to the next start date.

Data on different occupations. Some employees may have completed their employment and later joined them. They should be counted as two different activities (example ID 5). Some people have different types of employment, working one after another (enddate and startdate from neck to neck), in this case it should be considered as one activity in general (example ID 30).

A busy period that has not yet ended has an enddate value of null.

Some examples probably enlighten:

declare @t as table  (employmentid int, startdate datetime, enddate datetime)

insert into @t values
(5, '2007-12-03', '2011-08-26'),
(5, '2013-05-02', null),
(30, '2006-10-02', '2011-01-16'),
(30, '2011-01-17', '2012-08-12'),
(30, '2012-08-13', null),
(66, '2007-09-24', null)

-- expected outcome
EmploymentId StartDate   EndDate
5            2007-12-03  2011-08-26
5            2013-05-02  NULL
30           2006-10-02  NULL
66           2007-09-24  NULL

I tried different methods of "islands and spaces", but could not crack it.

Answer 1

, 31211231, - " ". , , , .

, , ( ). - . GROUP BY , ANCHOR (, ).

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SQL Fiddle

MS SQL Server 2008:

create table Tbl (
  employmentid int,
  startdate datetime,
  enddate datetime);

insert Tbl values
(5, '2007-12-03', '2011-08-26'),
(5, '2013-05-02', null),
(30, '2006-10-02', '2011-01-16'),
(30, '2011-01-17', '2012-08-12'),
(30, '2012-08-13', null),
(66, '2007-09-24', null);

/*
-- expected outcome
EmploymentId StartDate   EndDate
5            2007-12-03  2011-08-26
5            2013-05-02  NULL
30           2006-10-02  NULL
66           2007-09-24  NULL
*/

1:

;with cte as (
   select a.employmentid, a.startdate, a.enddate
     from Tbl a
left join Tbl b on a.employmentid=b.employmentid and a.startdate-1=b.enddate
    where b.employmentid is null
    union all
   select a.employmentid, a.startdate, b.enddate
     from cte a
     join Tbl b on a.employmentid=b.employmentid and b.startdate-1=a.enddate
)
   select employmentid,
          startdate,
          nullif(max(isnull(enddate,'32121231')),'32121231') enddate
     from cte
 group by employmentid, startdate
 order by employmentid

:

| EMPLOYMENTID |                        STARTDATE |                       ENDDATE |
-----------------------------------------------------------------------------------
|            5 |  December, 03 2007 00:00:00+0000 | August, 26 2011 00:00:00+0000 |
|            5 |       May, 02 2013 00:00:00+0000 |                        (null) |
|           30 |   October, 02 2006 00:00:00+0000 |                        (null) |
|           66 | September, 24 2007 00:00:00+0000 |                        (null) |

Answer 2

SET NOCOUNT ON

DECLARE @T TABLE(ID INT,FromDate DATETIME, ToDate DATETIME)

INSERT INTO @T(ID,FromDate,ToDate)
SELECT 1,'20090801','20090803' UNION ALL
SELECT 2,'20090802','20090809' UNION ALL
SELECT 3,'20090805','20090806' UNION ALL
SELECT 4,'20090812','20090813' UNION ALL
SELECT 5,'20090811','20090812' UNION ALL
SELECT 6,'20090802','20090802'


SELECT ROW_NUMBER() OVER(ORDER BY s1.FromDate) AS ID,
       s1.FromDate, 
       MIN(t1.ToDate) AS ToDate 
FROM @T s1 
INNER JOIN @T t1 ON s1.FromDate <= t1.ToDate 
  AND NOT EXISTS(SELECT * FROM @T t2 
                 WHERE t1.ToDate >= t2.FromDate
                   AND t1.ToDate < t2.ToDate) 
WHERE NOT EXISTS(SELECT * FROM @T s2 
                 WHERE s1.FromDate > s2.FromDate
                   AND s1.FromDate <= s2.ToDate) 
GROUP BY s1.FromDate 
ORDER BY s1.FromDate

Answer 3

Modified script to combine all overlapping periods.
For example
01.01.2001-01.01.2010
05.05.2005-05.05.2015

will give one period:
01.01.2001-05.05.2015

tbl.enddate should be completed

;WITH cte
  AS(
SELECT
  a.employmentid
  ,a.startdate
  ,a.enddate
from tbl a
left join tbl c on a.employmentid=c.employmentid
    and a.startdate > c.startdate
    and a.startdate <= dateadd(day, 1, c.enddate)
WHERE c.employmentid IS NULL

UNION all

SELECT
  a.employmentid
  ,a.startdate
  ,a.enddate
from cte a
inner join tbl c on a.startdate=c.startdate
    and (c.startdate = dateadd(day, 1, a.enddate) or (c.enddate > a.enddate and c.startdate <= a.enddate))
)
select distinct employmentid,
          startdate,
          nullif(max(enddate),'31.12.2099') enddate
from cte
group by employmentid, startdate