SQL SUM and divide linked tables - mysql

Question

I have the following tables:
create table Cars
(
CarID int,
CarType varchar(50),
PlateNo varchar(20),
CostCenter varchar(50),
);
insert into Cars (CarID, CarType, PlateNo, CostCenter) values
(1,'Coupe','BC18341','CALIFORNIA'),
(2,'Hatchback','AU14974','DAKOTA'),
(3,'Hatchback','BC49207','NYC'),
(4,'SUV','AU10299','FLORIDA'),
(5,'Coupe','AU32703','NYC'),
(6,'Coupe','BC51719','CALIFORNIA'),
(7,'Hatchback','AU30325','IDAHO'),
(8,'SUV','BC52018','CALIFORNIA');
create table Invoices
(
InvoiceID int,
InvoiceDate date,
CostCenterAssigned bit,
InvoiceValue money
);
insert into Invoices (InvoiceID, InvoiceDate, CostCenterAssigned, InvoiceValue) values
(1, '2021-01-02', 0, 978.32),
(2, '2021-01-15', 1, 168.34),
(3, '2021-02-28', 0, 369.13),
(4, '2021-02-05', 0, 772.81),
(5, '2021-03-18', 1, 469.37),
(6, '2021-03-29', 0, 366.83),
(7, '2021-04-01', 0, 173.48),
(8, '2021-04-19', 1, 267.91);
create table InvoicesCostCenterAllocations
(
InvoiceID int,
CarLocation varchar(50)
);
insert into InvoicesCostCenterAllocations (InvoiceID, CarLocation) values
(2, 'CALIFORNIA'),
(2, 'NYC'),
(5, 'FLORIDA'),
(5, 'NYC'),
(8, 'DAKOTA'),
(8, 'CALIFORNIA'),
(8, 'IDAHO');
How can I calculate the total invoice values allocated to that car based on its cost center?
If the invoice is allocated to cars in specific cost centers, then the CostCenterAssigned column is set to true and the cost centers are listed in the InvoicesCostCenterAllocations table linked to the Invoices table by the InvoiceID column. If there is no cost center allocation (CostCenterAssigned column is false) then the invoice value is divided by the total number of cars and summed up.
The sample data in Fiddle: http://sqlfiddle.com/#!18/9bd18/3

Answer 1

The data structure here isn't perfect, hence we need some extra code to solve for this. I needed to gather the amount of cars in each location, as well as to allocate the amounts for each invoice, depending on whether or not it was assigned to a location. I broke out the totals for each invoice type so that you can see the components which are being put together, you won't need those in your final result.
;WITH CarsByLocation AS(
SELECT
CostCenter
,COUNT(*) AS Cars
FROM Cars
GROUP BY CostCenter
UNION ALL
SELECT
''
,COUNT(*) AS Cars
FROM Cars
),CostCenterAssignedInvoices AS (
SELECT
InvoicesCostCenterAllocations.CarLocation
,SUM(invoicevalue) / CarsByLocation.cars AS InvoiceTotal
FROM Invoices
INNER JOIN InvoicesCostCenterAllocations ON invoices.InvoiceID = InvoicesCostCenterAllocations.InvoiceID
INNER JOIN CarsByLocation on InvoicesCostCenterAllocations.CarLocation = CarsByLocation.CostCenter
WHERE CostCenterAssigned = 1 --Not needed, put here for clarification
GROUP BY InvoicesCostCenterAllocations.CarLocation,CarsByLocation.Cars
),UnassignedInvoices AS (
SELECT
'' AS Carlocation
,SUM(invoicevalue)/CarsByLocation.Cars InvoiceTotal
FROM Invoices
INNER JOIN CarsByLocation on CarsByLocation.CostCenter = ''
WHERE CostCenterAssigned = 0
group by CarsByLocation.Cars
)
SELECT
Cars.*
,cca.InvoiceTotal AS AssignedTotal
,ui.InvoiceTotal AS UnassignedTotal
,cca.InvoiceTotal + ui.InvoiceTotal AS Total
FROM Cars
LEFT OUTER JOIN CostCenterAssignedInvoices CCA ON Cars.CostCenter = CCA.CarLocation
LEFT OUTER JOIN UnassignedInvoices UI ON UI.Carlocation = ''
ORDER BY
Cars.CostCenter
,Cars.PlateNo;