Question

I have a table which is filled with float values. I need to calculate the number of results grouped by their distribution around the mean value (Gaussian Distribution). Basically, it is calculated like this:

SELECT COUNT(*), FloatColumn - AVG(FloatColumn) - STDEV(FloatColumn) 
FROM Data 
GROUP BY FloatColumn - AVG(FloatColumn) - STDEV(FloatColumn)

But for obvious reasons, SQL Server gives this error: Cannot use an aggregate or a subquery in an expression used for the group by list of a GROUP BY clause.

My question is, can I somehow leave this computation to SQL Server? Or do I have to do it the old fashioned way? Retrieve all the data, and do the calculation myself?

Answer 1

To get the aggregate of the whole set you can use an empty OVER clause

WITH T(Result)
     AS (SELECT FloatColumn - Avg(FloatColumn) OVER() - Stdev(FloatColumn) OVER ()
         FROM   Data)
SELECT Count(*),
       Result
FROM   T
GROUP  BY Result