Find Range of continous values

There are many ways to find out gaps & range, but this standard gaps-and-island solution that I found on net is coolest one. Basic idea of this solution is to group by (value minus row_number), since that is invariant within a consecutive sequence. The start and end dates are just the MIN() and MAX() of the group.

The value could be int or date.

DECLARE @data TABLE (i INT)

INSERT INTO @data
VALUES (1)
 ,(2)
 ,(4)
 ,(5)
 ,(10)
 ,(11)
 ,(15)
 ,(16)
 ,(17)
 ,(18)
 ,(19)
 ,(20)
 ,(21);

WITH tab
AS (
 SELECT i d
  ,ROW_NUMBER() OVER (
   ORDER BY i
   ) r
 FROM @data
 )
SELECT min(d)
 ,max(d)
FROM tab
GROUP BY d - r

Output: 

Hope it helps