declare @t table(n int,id int)
insert into @t (n,id)
values
 (1,1)
,(2,1)
,(3,1)
,(4,2)
,(5,2)
,(6,3)
,(7,1)
,(8,1)
,(9,2);

WITH CTE AS(SELECT rn=ROW_NUMBER()OVER(ORDER BY n)-ROW_NUMBER()OVER(PARTITION BY id ORDER BY n),* FROM @t)
SELECT n=MIN(n), id=MIN(id)
FROM CTE
GROUP BY rn,id
ORDER BY n;