Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

calculating a weighted average in SQL, SSRS

Posted on 2010-11-14
7
Medium Priority
?
4,516 Views
Last Modified: 2012-05-10
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.

0
Comment
Question by:erp1022
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
  • 2
  • +1
7 Comments
 
LVL 79

Expert Comment

by:arnold
ID: 34131907
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.
 
0
 
LVL 93

Assisted Solution

by:Patrick Matthews
Patrick Matthews earned 800 total points
ID: 34131921
I would create the weighted average in your underlying query.

This article shows how to calculate a weighted average; while it is done for Access, the logic for SQL Server is much the same, except you would use CASE instead of IIf:

SELECT {group by columns if desired,} (CASE WHEN MIN([WeightColumn]) >=0 AND
    MAX([WeightColumn]) > 0 THEN SUM([WeightColumn] * [ValueColumn]) ELSE NULL END) /
    SUM([WeightColumn]) AS WtdAvg
FROM {tables}
{GROUP BY {group by columns}}

Open in new window


Patrick
0
 

Author Comment

by:erp1022
ID: 34132408
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?
0
Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

 
LVL 93

Expert Comment

by:Patrick Matthews
ID: 34132429
Perhaps it would be best if you could work up some sample source data, and then the output you would expect given that input.
0
 

Author Comment

by:erp1022
ID: 34132779
Please see attachment...
Weighted-Average.xls
0
 
LVL 41

Expert Comment

by:ralmada
ID: 34136671
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

Open in new window

0
 
LVL 41

Accepted Solution

by:
ralmada earned 1200 total points
ID: 34136969
sorry actually it should be
select 	transtype,
	count(items),
	sum(amount),
	sum(amount) * count(items) * 1.0 / sum(amount) as weight_avg
from yourtable
group by transtype
with rollup

Open in new window

0

Featured Post

Will your db performance match your db growth?

In Percona’s white paper “Performance at Scale: Keeping Your Database on Its Toes,” we take a high-level approach to what you need to think about when planning for database scalability.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Windocks is an independent port of Docker's open source to Windows.   This article introduces the use of SQL Server in containers, with integrated support of SQL Server database cloning.
Ready to get certified? Check out some courses that help you prepare for third-party exams.
Via a live example, show how to backup a database, simulate a failure backup the tail of the database transaction log and perform the restore.
Via a live example, show how to setup several different housekeeping processes for a SQL Server.

722 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question