SELECT value - (previous.value) FROM table

select t1.value - t2.value from table t1, table t2
where t1.primaryKey = t2.primaryKey - 1

select  rank() OVER (ORDER BY id) as 'Rank', value into temp1 from t

select t1.value - t2.value from temp1 t1, temp1 t2
where t1.Rank = t2.Rank - 1

drop table temp1

SELECT  value - (
        SELECT  TOP 1 value
        FROM    mytable m2
        WHERE   m2.col1 < m1.col1 OR (m2.col1 = m1.col1 AND m2.pk < m1.pk)
        ORDER BY
                col1, pk
        )
FROM mytable m1
ORDER BY
      col1, pk

declare @temp (value int, primaryKey int, tempid int identity)
insert value, primarykey from mytable order by  primarykey

select t1.value - t2.value from @temp  t1
join @temp  t2
on t1.tempid = t2.tempid - 1