I need your help. Database: SQL SERVER 2008R2 I want to calculte for a year and a week the average of value of the 4 last weeks. I have data a table like that: YEAR WEEKS VALUE 2012 1 3000 2012 2 5000 2012 3 6000 2012 4 7000 2012 5 8000 2012 6 9000 2012 7 1000 2012 8 6000 2012 9 9000 2012 10 4000 And I want that : YEAR WEEKS VALUE 2012 1 ( Average value for week 49, 50, 51, 52 for the year 2011) 2012 2 ( Average value for week 50, 51, 52 for the year 2011 and week 1 for the year 2012) 2012 3 ( Average value for week 51, 52 for the year 2011 and week 1, 2 for the year 2012) 2012 4 ( Average value for week 52 for the year 2011 and week 1, 2, 3 for the year 2012) 2012 5 5250 - ( Average value for week 1, 2, 3 , 4 for the year 2012) 2012 6 6500 - ( Average value for week 2, 3 , 4, 5 for the year 2012) Thank U for your help