SUM multiple tables GROUP BY column - sql

Question

I have the following SQL Server tables:
create table Cars
(
CarID int,
CarType varchar(50),
PlateNo varchar(20)
);
create table Fuelings
(
CarID int,
FuelingDate date,
Odometer int,
Quantity decimal,
Cost money
);
create table Maintenances
(
CarID int,
MaintenanceDate date,
MaintenanceCost money
);
I'm having problems calculating the fuel consumption grouped by the column CarType. To get the fuel consumption I want to calculate the distance and fuel quantity for each car, then sum that up grouped by the column CarType.
What I have now:
SELECT DISTINCT C.CarType AS [Car type],
SUM(M.MaintenanceCost) AS [Maintenance],
SUM(F.Cost) AS [Fuel],
(MAX(Odometer)-MIN(Odometer)) AS [Distance],
(SUM(Quantity)*100)/(MAX(Odometer)-MIN(Odometer)) AS [L/100km]
FROM Cars AS C
LEFT JOIN Maintenances AS M ON M.CarID=C.CarID
AND M.MaintenanceDate BETWEEN '2021-01-01 00:00:00' AND '2021-01-31 23:59:29'
LEFT JOIN Fuelings AS F ON F.CarID=C.CarID
AND F.FuelingDate BETWEEN '2021-01-01 00:00:00' AND '2021-01-31 23:59:29'
GROUP BY C.CarType
Desired result for type 'SUV':
Total fuel quantity: 301
Total distance: 1600
Consumption: 18,8125
See here: http://sqlfiddle.com/#!18/2636c/18

Answer 1

I used a common table expression cte_car to make a first grouping and get all the details of a single car. Then a final grouping is done to get the totals accross the car types.
Sample data
I left out the Maintenances table because it is not needed for the consumptions.
create table Cars
(
CarID int,
CarType varchar(50),
PlateNo varchar(20)
);
insert into Cars (CarID, CarType, PlateNo) values
(1,'Coupe','BC18341'),
(2,'Hatchback','AU14974'),
(3,'Hatchback','BC49207'),
(4,'SUV','AU10299'),
(5,'Coupe','AU32703'),
(6,'Coupe','BC51719'),
(7,'Hatchback','AU30325'),
(8,'SUV','BC52018');
create table Fuelings
(
CarID int,
FuelingDate date,
Odometer int,
Quantity decimal,
Cost money
);
insert into Fuelings (CarID, FuelingDate, Odometer, Quantity, Cost) values
(1,'2021-01-02', 124520, 53.28, 78.32),
(1,'2021-01-15', 124810, 49.17, 68.34),
(1,'2021-01-28', 125130, 51.74, 69.13),
(2,'2021-01-05', 344380, 49.10, 72.81),
(2,'2021-01-18', 344540, 54.98, 69.37),
(2,'2021-01-29', 344990, 52.76, 66.83),
(3,'2021-01-01', 874200, 45.27, 73.48),
(3,'2021-01-19', 874770, 46.75, 67.91),
(3,'2021-01-26', 874930, 52.15, 75.50),
(4,'2021-01-03', 414190, 50.88, 71.72),
(4,'2021-01-14', 414400, 51.94, 68.15),
(4,'2021-01-29', 415140, 48.30, 77.82),
(5,'2021-01-06', 294240, 48.15, 71.48),
(5,'2021-01-19', 294680, 53.86, 66.80),
(5,'2021-01-30', 294890, 51.54, 74.31),
(6,'2021-01-01', 934220, 49.26, 69.98),
(6,'2021-01-18', 934520, 51.35, 71.50),
(6,'2021-01-25', 934970, 54.63, 65.72),
(7,'2021-01-05', 584110, 51.42, 74.29),
(7,'2021-01-22', 584430, 49.36, 69.95),
(7,'2021-01-31', 584750, 49.84, 73.18),
(8,'2021-01-02', 654280, 53.87, 77.75),
(8,'2021-01-17', 654730, 45.32, 67.48),
(8,'2021-01-29', 654930, 50.75, 69.80);
Solution
with cte_car as
(
select c.CarId,
c.CarType,
max(f.Odometer) - min(f.Odometer) as CarDistance,
sum(f.Quantity) as CarQuantity
from Cars c
join Fuelings f
on f.CarId = c.CarId
group by c.CarId,
c.CarType
)
select cc.CarType,
sum(cc.CarDistance) as TotalDistance,
sum(cc.CarQuantity) as TotalQuantity,
sum(cc.CarQuantity) * 100.0 / sum(cc.CarDistance) as TotalConsumption
from cte_car cc
group by cc.CarType;
Result
CarType TotalDistance TotalQuantity TotalConsumption
------- ------------- ------------- ----------------
Coupe 2010 463 23.034825
Hatchback 1980 451 22.777777
SUV 1600 301 18.8125
Fiddle to see things in action.