Merge overlapping date intervals

Question

Is there a better way of merging overlapping date intervals?
The solution I came up with is so simple that now I wonder if someone else has a better idea of how this could be done.

/***** DATA EXAMPLE *****/
DECLARE @T TABLE (d1 DATETIME, d2 DATETIME)
INSERT INTO @T (d1, d2)
        SELECT '2010-01-01','2010-03-31' UNION SELECT '2010-04-01','2010-05-31' 
  UNION SELECT '2010-06-15','2010-06-25' UNION SELECT '2010-06-26','2010-07-10' 
  UNION SELECT '2010-08-01','2010-08-05' UNION SELECT '2010-08-01','2010-08-09' 
  UNION SELECT '2010-08-02','2010-08-07' UNION SELECT '2010-08-08','2010-08-08' 
  UNION SELECT '2010-08-09','2010-08-12' UNION SELECT '2010-07-04','2010-08-16' 
  UNION SELECT '2010-11-01','2010-12-31' UNION SELECT '2010-03-01','2010-06-13' 

/***** INTERVAL ANALYSIS *****/
WHILE (1=1)  BEGIN
  UPDATE t1 SET t1.d2 = t2.d2
  FROM @T AS t1 INNER JOIN @T AS t2 ON 
            DATEADD(day, 1, t1.d2) BETWEEN t2.d1 AND t2.d2 
  IF @@ROWCOUNT = 0 BREAK
END

/***** RESULT *****/
SELECT StartDate = MIN(d1) , EndDate = d2
FROM @T
GROUP BY d2
ORDER BY StartDate, EndDate

/***** OUTPUT *****/
/*****
StartDate   EndDate
2010-01-01  2010-06-13 
2010-06-15  2010-08-16 
2010-11-01  2010-12-31 
*****/

Answer 1

You asked this back in 2010 but don't specify any particular version.

An answer for people on SQL Server 2012+

WITH T1
     AS (SELECT *,
                MAX(d2) OVER (ORDER BY d1) AS max_d2_so_far
         FROM   @T),
     T2
     AS (SELECT *,
                CASE
                  WHEN d1 <= DATEADD(DAY, 1, LAG(max_d2_so_far) OVER (ORDER BY d1))
                    THEN 0
                  ELSE 1
                END AS range_start
         FROM   T1),
     T3
     AS (SELECT *,
                SUM(range_start) OVER (ORDER BY d1) AS range_group
         FROM   T2)
SELECT range_group,
       MIN(d1) AS d1,
       MAX(d2) AS d2
FROM   T3
GROUP  BY range_group 

Which returns

+-------------+------------+------------+
| range_group |     d1     |     d2     |
+-------------+------------+------------+
|           1 | 2010-01-01 | 2010-06-13 |
|           2 | 2010-06-15 | 2010-08-16 |
|           3 | 2010-11-01 | 2010-12-31 |
+-------------+------------+------------+

DATEADD(DAY, 1 is used because your desired results show you want a period ending on 2010-06-25 to be collapsed into one starting 2010-06-26. For other use cases this may need adjusting.