SQL Calculate Percentage in Group By

Question

I have an SQL query that is used as the basis for a report. The report shows the amount of fuel used grouped by Year, Month and Fuel Type. I would like to calculate the percentage of the total for each fuel type, but I'm not having much luck. In order to calculate the percentage of the whole, I need to be able to get the total amount of fuel used regardless of the group it is in and I can't seem to figure out how to do this. Here is my query:

SELECT Year([DT1].[TransactionDate]) AS [Year], Month([DT1].[TransactionDate]) AS [Month], DT1.FuelType, Format(Sum(DT1.Used),"#.0") AS [Total Used],    
FROM (SELECT TransactionDate, FuelType, Round([MeterAfter]-[MeterBefore],2) AS Used FROM FuelLog)  AS DT1
WHERE (((DT1.TransactionDate) Between [Start Date] And [End Date]))
GROUP BY Year([DT1].[TransactionDate]), Month([DT1].[TransactionDate]), DT1.FuelType
ORDER BY Year([DT1].[TransactionDate]), Month(DT1.TransactionDate), DT1.FuelType;

I tried adding the following as a subquery but I get an error saying the subquery returns more than one result.

(SELECT Sum(Round([MeterAfter]-[MeterBefore],2)) AS Test
FROM Fuellog 
WHERE Year([Year]) and Month([Month])
GROUP BY Year([TransactionDate]), Month([TransactionDate]))

Once I get the total of all fuel I will need to divide the amount of fuel used by the total amount of both fuel types. Should I be approaching this a different way?

Answer 1

You need to join to the totals -- something like this (untested might have typos)

SELECT 
  Year([DT1].[TransactionDate]) AS [Year],
  Month([DT1].[TransactionDate]) AS [Month], 
  DT1.FuelType, 
  Format(Sum(DT1.Used),"#.0") AS [Total Used],    
  (Sum(DT1.Used) / FT.Total) * 100 AS Percent
FROM (
  SELECT 
    TransactionDate,
    FuelType, 
    Round([MeterAfter]-[MeterBefore],2) AS Used 
  FROM FuelLog
)  AS DT1
JOIN (
  SELECT
     Sum(Round([MeterAfter]-[MeterBefore],2)) AS Total
     FuelType
  FROM Fuellog 
  WHERE TransactionDate Between [Start Date] And [End Date]
  GROUP BY FuelType  
) FT ON DT1.FuelType = FT.FeulType
WHERE DT1.TransactionDate Between [Start Date] And [End Date]
GROUP BY Year([DT1].[TransactionDate]), Month([DT1].[TransactionDate]), DT1.FuelType, FT.Total
ORDER BY Year([DT1].[TransactionDate]), Month(DT1.TransactionDate), DT1.FuelType, FT.Total;

Answer 2

Try this

SELECT A.[Year]
      ,A.[Month]
      ,A.[FuelType]
      ,A.[Total Used]
      ,(A.[Total Used] / B.[Total By Year Month]) * 100 AS Percentage
  FROM
(
  SELECT Year([DT1].[TransactionDate]) AS [Year]
     , Month([DT1].[TransactionDate]) AS [Month]
     , DT1.FuelType
     , Format(Sum(DT1.Used),"#.0") AS [Total Used]
  FROM (
         SELECT TransactionDate
              , FuelType
              , Round([MeterAfter]-[MeterBefore],2) AS Used 
           FROM FuelLog
       )  AS DT1
WHERE (((DT1.TransactionDate) Between [Start Date] And [End Date]))
GROUP BY Year([DT1].[TransactionDate]), Month([DT1].[TransactionDate]),     DT1.FuelType
ORDER BY Year([DT1].[TransactionDate]), Month(DT1.TransactionDate),     DT1.FuelType
  ) A
INNER JOIN 
  (
    SELECT Sum(Round([MeterAfter]-[MeterBefore],2)) AS [Total By Year Month]
         , Year([TransactionDate]) AS [Year]
         , Month([TransactionDate])) AS [Month]
      FROM Fuellog 
     GROUP
        BY Year([TransactionDate])
         , Month([TransactionDate]))
  ) B
   ON A.[Year] = B.[Year]
  AND A.[Month] = B.[Month]