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How can I calculate average per month for each row?

Posted on 2004-04-28
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Last Modified: 2011-10-03
I have a table that looks something like this:

SalesArea   |   ProductID   |   Sold       |     TotalDate
     1                     a                432               4/8/2004
     1                     b                328               4/8/3004
     1                     a                264               4/15/2004
     1                     b                128               4/15/3004
     2                     a                763               4/8/2004
     2                     b                436               4/8/3004
     2                     a                458               4/15/2004
     2                     b                274               4/15/3004

I want to write a SELECT statement that returns the info listed above along with the average SOLD per SalesArea per ProductID per Month.

So the first row returned would look like this:
SalesArea   |   ProductID   |   Sold       |     TotalDate      |    AverageForMonth
     1                     a                432               4/8/2004               348

AverageForMonth=Avg of SOLD from rows 1 and 3 since they are both the same SalesArea, ProductID and in the same Month (and year)


Thanks,
John
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Question by:jholton
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6 Comments
 
LVL 70

Accepted Solution

by:
Scott Pletcher earned 240 total points
ID: 10940620
Please try this (*not* tested yet):

SELECT yt.*, yt2.AverageForMonth
FROM yourTable yt
INNER JOIN (
      SELECT SalesArea, ProductId, CONVERT(CHAR(7), TotalDate, 120) AS [Yr-Mth], AVG(Sold) AS AverageForMonth
      FROM yourTable yt2
      GROUP BY SalesArea, ProductId, CONVERT(CHAR(7), TotalDate, 120)
) AS yt2 ON yt.SalesArea = yt2.SalesArea AND yt.ProductId = yt2.ProductId AND
      CONVERT(CHAR(7), yt.TotalDate, 120) = yt2.[Yr-Mth]
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LVL 70

Expert Comment

by:Scott Pletcher
ID: 10940653
Seems to be working OK ... as longs as NULLs aren't an issue.  If that needs to be addressed, please let me know.
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LVL 26

Assisted Solution

by:Hilaire
Hilaire earned 160 total points
ID: 10940699
try this
select a.SalesArea, a.ProductID, a.Sold, a.TotalDate, avg(b.Sold) as AverageForMonth
from <YourTable> a
inner join <YourTable> b on a.SalesArea = b.SalesArea and a.ProductID = b.ProductID
and month(a.TotalDate) = month(b.TotalDate) and year(a.TotalDate) = year(b.TotalDate)
group by a.SalesArea, a.ProductID, a.Sold, a.TotalDate

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LVL 9

Expert Comment

by:SoftEng007
ID: 10940954
Something a little faster,


select datename(month,totaldate) [Month],salesarea,productid,avg(sold)
from <tablename>
group by datename(month,totaldate),salesarea,productid
order by datename(month,totaldate),salesarea,productid
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LVL 70

Expert Comment

by:Scott Pletcher
ID: 10941236
Faster, but without the detail requested in the original post, specifically the individual dates and sold amounts.

My inner subquery could be pulled out and would give you the same result, except that it matches by both year and month, rather than just month, so more than 12 months could be viewed.
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LVL 9

Expert Comment

by:SoftEng007
ID: 10942467
Aboslutly correct Scott.
I missed the details..
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