weighted average

I have the following table

A  B   ID
1  8    s
4  9    x
5  10   m
6  11  n
7  12   o

I want to calculated weighte average as follows
only for IDs  s and x i want to find weighted average 1/sum(all Bs) and 4/sum of all Bs

what is the query for this?
camper12Asked:
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Rey Obrero (Capricorn1)Commented:
not really sure what you exactly are looking for, but give this a try.

SELECT tweight.ID, IIf([ID]="S",1/Sum(B),0) AS Expr1, IIf([ID]="X",4/Sum(B),0) AS Expr2
FROM tweight
GROUP BY tweight.ID
HAVING (((tweight.ID) In ("s","x")));

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TONY TAYLORCommented:
If I understand you correctly, then you want to weight average the table based on the ID based upon the sum of the values in Column B.  For "s" you want it to weight with a numerator of 1 and for "x" you want a numerator of 4.  All others I am assuming you want as the sum of the value of B for that given ID.  The query is below.  To add more IDs and their weights you can union them on WEIGHT_AMT.

SELECT MT.*, CASE WHEN WEIGHT_AMT.ID IS NULL THEN POWER(SUM_OF_B.SUM_OF_B, 2) ELSE WEIGHT_AMT.WEIGHT_AMT END / CAST(SUM_OF_B.SUM_OF_B AS decimal) AS WEIGHTED_AVERAGE
FROM 
	MyTable MT
	LEFT JOIN (SELECT 's' AS ID, 1 AS WEIGHT_AMT UNION SELECT 'x', 4) WEIGHT_AMT ON MT.ID = WEIGHT_AMT.ID 
	OUTER APPLY (SELECT SUM(B) AS SUM_OF_B FROM MyTable WHERE ID = MT.ID) SUM_OF_B 

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Rey has got a great point in his writing.  He supplied Access SQL, I supplied SQL Server SQL.  Question was in both categories and indeterminate as to where the query is needed.
Dale FyeOwner, Developing Solutions LLCCommented:
With just this simple dataset, Rey's recommendation would be fine, but with a more exhaustive recordset, I think something like the following would be quicker:

SELECT A.ID, A.[A]/B.[Total]
FROM yourTable as A, (SELECT SUM(B) as Total FROM yourTable) as B
WHERE A.ID IN ("s", "x")
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