Question

Say I have table and these are its sample rows

ChangeID    Change
   1         102
   2         105
   3         107
   4         110

The change formula is

(CurrentRowChange - PreviousRowChange) / PreviousRowChange

Hence:

• for 1st row it should be 0
• for 2nd row it should be (105 - 102) / 102

and so on. How can I efficiently write this formula in SQL?

I know I can write a scalar function and then do a RowNumber and order By ChangeID and fetch the row number’s Change value and then find the current row number – 1 and then fetch that row’s Change value and do a divide.

Is there any better way to achieve this?

Answer 1

give this a try, assuming that CHANGEID can be deleted and it is IDENTITY.

WITH changeList
AS
(
    SELECT ChangeID, [Change],
           (ROW_NUMBER() OVER (ORDER BY ChangeID ASC)) -1 AS rn
    FROM   TableName
),
normalList
AS
(
    SELECT ChangeID, [Change],
           (ROW_NUMBER() OVER (ORDER BY ChangeID ASC)) AS rn
    FROM   TableName
)
SELECT a.ChangeID, a.[Change], 
       COALESCE((a.Change - b.change) / (b.change * 1.0),0) result
FROM   changeList a
       LEFT JOIN normalList b
          ON a.rn = b.rn

• SQLFiddle Demo