10 Month average

I'm replacing an Excel spreadsheet wit开发者_StackOverflowh a Microsoft SQL Server 2008 database and need to calculate this:

=AVERAGE(IF((A:A>A4-304)*(A:A<=A4),G:G))

Where column A is the date and column G is the value. The heading for this field is:

10 month simple moving average

I suppose I will use something like:

SELECT RawData.* 
,(SELECT Sum(X.AdjClose) AS SumAdjClose
    FROM RawData X
    WHERE DATEDIFF(d,X.RawDate,RawData.RawDate) <= 304
) AS SumAdjClose
FROM RawData

---

In SQL Server one option is to make the filters in the WHERE clause and the average in the SELECT

select  avg(ValueCol)
from    Table1
where   DateCol between @Date-304 and @Date

Another option, in the same logic of the excel could be:

select  avg(case when DateCol between @Date-304 and @Date then ValueCol else null)
from    Table1