Sql Trend line by departments - sql

Question

I'm using the example of how to create a sql trend line on a report using the below link.
https://www.mssqltips.com/sqlservertip/3432/add-a-linear-trendline-to-a-graph-in-sql-server-reporting-services/
I've got it all up and running but I want to work out the trend by departments also. However its just merging all the data into one final value, I think its the below section of code that needs altering to calculate the sum by each of the departments I add in, but how best do I do this?
-- calculate sample size and the different sums
SELECT
#sample_size = COUNT(*)
,#sumX = SUM(ID)
,#sumY = SUM([OrderQuantity])
,#sumXX = SUM(ID*ID)
,#sumYY = SUM([OrderQuantity]*[OrderQuantity])
,#sumXY = SUM(ID*[OrderQuantity])
FROM #Temp_Regression;
-- output results
SELECT
SampleSize = #sample_size
,SumRID = #sumX
,SumOrderQty =#sumY
,SumXX = #sumXX
,SumYY = #sumYY
,SumXY = #sumXY;
These variables are then used to work out the trend line:
-- calculate the slope and intercept
SET #slope = CASE WHEN #sample_size = 1
THEN 0 -- avoid divide by zero error
ELSE (#sample_size * #sumXY - #sumX * #sumY) / (#sample_size * #sumXX - POWER(#sumX,2))
END;
SET #intercept = (#sumY - (#slope*#sumX)) / #sample_size;

Answer 1

You need to add departments column in SELECT & GROUP BY
SELECT departments,
SampleSize = Count(*),
SumRID = Sum(ID),
SumOrderQty = Sum([OrderQuantity]),
SumXX = Sum(ID * ID),
SumYY = Sum([OrderQuantity] * [OrderQuantity]),
SumXY = Sum(ID * [OrderQuantity])
FROM #Temp_Regression
GROUP BY departments
Here is the easier way to calculate slope & intercept for all departments
;WITH cte
AS (SELECT departments,
sample_size = Count(*),
sumX = Sum(ID),
sumY = Sum([OrderQuantity]),
sumXX = Sum(ID * ID),
sumYY = Sum([OrderQuantity] * [OrderQuantity]),
sumXY = Sum(ID * [OrderQuantity])
FROM #Temp_Regression
GROUP BY departments),
slope
AS (SELECT departments,
Sample_Size,
sumX,
sumY,
slope = CASE
WHEN sample_size = 1 THEN 0 -- avoid divide by zero error
ELSE ( sample_size * sumXY - sumX * sumY ) / ( sample_size * sumXX - Power(sumX, 2) )
END
FROM cte)
SELECT departments,
slope,
intercept = ( sumY - ( slope * sumX ) ) / sample_size
FROM slope