Question

I have a table in which i have columns like :

ItemId   Date        CountUser       CountUserPast7Days
1        20120101    20              null
1        20120102    15              null
1        20120208    12              null
2        20120209    65              null
2        20120611    32              null
2        20120615    20              null
3        20120901    45              null

I want to write an query to update CountUserPast7Days based on – group by the data on two parameters – ItmeId and Date(past 7 days) and sum the column CountUser. So the data should look like –

ItemId   Date        CountUser    CountUserPast7Days
1        20120101    20           20 
1        20120102    15           35 
1        20120208    12           27 
2        20120209    65           65
2        20120611    32           32
2        20120615    20           52
3        20120901    45           45

Answer 1

Your example output is buggy, since there is more than a month between 2012/01/02 and 2012/02/08, but I got your point all the same. What you are looking for is a self-join:

SELECT S1.Item, S1.Date, SUM(S2.Count) As CountPast7 FROM SlidingHitCount S1
  INNER JOIN SlidingHitCount S2 on S1.Item = S2.Item
WHERE S2.Date BETWEEN DATEADD(dd, -7, S1.Date) AND S1.Date
GROUP BY S1.Item, S1.Date

Obviously I called your table “SlidingHitCount.”