SQL Date Range Split

Question

Can you please let me know the SQL to split date ranges when they overlap?

Data (sample data with a date range and possibly other columns):

    Col1 FromDate ToDate
 1. 1    1/1/2008 31/12/2010
 2. 1    1/1/2009 31/12/2012
 3. 1    1/1/2009 31/12/2014

Output:

   Col1  From Date ToDate
1. 1     1/1/2008 31/12/2008 (from row 1 above)
2. 1     1/1/2009 31/12/2010 (from rows 1,2 and 3 above)
3. 1     1/1/2011 31/12/2012 (from rows 2 and 3 above)
4. 1     1/1/2013 31/12/2014 (from row 3 above)

Answer 1

This should do the trick (MySQL dialect, but easily adaptable)

Initial setup

SQL query: SELECT * FROM `test` LIMIT 0, 30 ;
Rows: 3
start       end
2008-01-01  2010-12-31
2009-01-01  2012-12-31
2009-01-01  2014-12-31

Query

SELECT 
  `start` , min( `end` )
FROM (
  SELECT t1.start, t2.end
  FROM test t1, test t2
  WHERE t1.start < t2.end
  UNION
  SELECT t1.end + INTERVAL 1 DAY , t2.end
  FROM test t1, test t2
  WHERE t1.end + INTERVAL 1 DAY < t2.end
  UNION
  SELECT t1.start, t2.start - INTERVAL 1 DAY
  FROM test t1, test t2
  WHERE t1.start < t2.start - INTERVAL 1 DAY
) allRanges
GROUP BY `start`

Result

start       min( `end` )
2008-01-01  2008-12-31
2009-01-01  2010-12-31
2011-01-01  2012-12-31
2013-01-01  2014-12-31

Answer 2

Skliwz's answer adapted for SQL Server:

DECLARE @DateTest TABLE 
(
    FromDate datetime,
    ToDate datetime 
)

insert into @DateTest (FromDate, ToDate)
(
select cast('1/1/2008' as datetime), cast('12/31/2010' as datetime)
union
select cast('1/1/2009' as datetime), cast('12/31/2012' as datetime)
union
select cast('1/1/2009' as datetime), cast('12/31/2014' as datetime)
)

SELECT 
  FromDate , min(ToDate)
FROM (
  SELECT t1.FromDate, t2.ToDate
  FROM 
    @DateTest t1, 
    @DateTest t2
  WHERE t1.FromDate < t2.ToDate

  UNION

  SELECT dateadd(DAY, 1, t1.ToDate), t2.ToDate
  FROM 
    @DateTest t1, 
    @DateTest t2
  WHERE dateadd(DAY, 1, t1.ToDate) < t2.ToDate
) allRanges
group by FromDate