# calculating a weighted average in SQL, SSRS

Hello Experts,

Does anyone know how to calculate a weighted average in SQL?

First I get the average of something: COUNT(transactions)/Fee = Average
Then to get the weighted average I would have to total the above values of 'Average' for the three different transactions types we use, and then divide that by the total count.

I cannot create a calculated field because in SSRS you can't use aggregate functions in a calc field. Also, in SSRS, I have tried creating an expression:

=(SUM((Fields!CRDTAMNT.Value/COUNT(Fields!Trans.Value))* COUNT(Fields!Trans.Value)))/COUNT(Fields!Trans.Value)

and I keep getting errors about nested aggregate functions.

So first of all, should I do this in my query or somewhere in SSRS?
Second of all, what is the code/syntax to achieve this?

Thanks.

arnold

You have the value and the weight in each row or you know the weights.
in either case you would first sum the weights into a variable and then use the formula of wight*value/sum(weights)

select @total_weight=sum(weights) from table;
select @weighted_average+=sum(weights*values/@total_weight) from table;

have not tried it such that not sure whether it is even valid.

SOLUTION
Patrick Matthews

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Okay now I'm really confused.

So if my weighted average is based on a count of transactions [COUNT(Trans)] * an amount, how would I write my code in SQL?
Perhaps it would be best if you could work up some sample source data, and then the output you would expect given that input.

Weighted-Average.xls
try this query
``````select 	transtype,
count(items),
sum(amount),
sum(amount * items) * 1.0 / sum(amount) as weight_avg
from yourtable
group by transtype
with rollup
``````