Using summed field in query twice with IIF statement - have I missed some syntax somewhere? - sql

Question

Having a bit of a problem with my code and can't figure out where I'm going wrong.
Essentially this query will return all employees for a given employer for a given year, along with the amount of their allowances, tax withheld, and gross payments they've received, and their Reportable Employer Superannuation Contributions (RESC).
RESC is any amounts (tblSuperPayments.PaymentAmount) paid over and above the superannuation guarantee, which is gross payments (sum of tblPayment.GrossPayment) * super rate (tblSuperRate.SuperRate). Otherwise, RESC is 0.
The data that I currently have in my tables is as follows
SUM(tblPayment.GrossPayment) = 1730
SUM(tblEmployee.TaxPayable) = 80
SUM(tblSuperPayments.PaymentAmount) = 500
tblSuperRate.SuperRate = 9.5%
Therefore my query should be returning an amount of RESC of 500-(1730*9.5%)= 335.65.
However, my query is currently returning $835.65 - meaning that (1730*9.5%) is returning -335.65.
I can't figure out where my logic is going wrong - it's probably something simple but I can't see it. I suspect that it might be summing tblPayment.GrossPayment twice (edited on request)
SELECT
tblEmployee.EmployeeID AS Id
SUM(tblPayment.Allowances) AS TotAllow,
SUM(tblPayment.TaxPayable) AS TotTax,
SUM(tblPayment.GrossPayment) AS TotGross,
(IIF
((SUM(tblSuperPayments.PaymentAmount)) <= (SUM(tblPayment.GrossPayment)*tblSuperRate.SuperRate),
0,
(SUM(tblSuperPayments.PaymentAmount) - (SUM(tblPayment.GrossPayment)*tblSuperRate.SuperRate))
)) As TotRESC
FROM
((tblEmployee
LEFT JOIN tblPayment // any reason for using left join over inner join
ON tblEmployee.EmployeeID = tblPayment.fk_EmployeeID)
LEFT JOIN tblSuperPayments // any reason for using left join over inner join
ON tblEmployee.EmployeeID = tblSuperPayments.fk_EmployeeID)
LEFT JOIN tblSuperRate // any reason for using left join over inner join
ON (tblPayment.PaymentDate <= tblSuperRate.TaxYearEnd) // these two conditions might be returning
AND (tblPayment.PaymentDate >= tblSuperRate.TaxYearStart) //two SuperRate rows because of using equals in both
WHERE
tblEmployee.fk_EmployerID = 1
GROUP BY
tblEmployee.EmployeeID,
tblSuperRate.SuperRate;

Answer 1

Looking at your query I recommend you to just group by primary key (EmployeeID) of tblEmployee and the use the result as a sub query and do a join later tham using many columns of tblEmployeein group by which might cause duplicate rows. I rewrote the query as I have mentioned above and added comments at places which might cause the error.
SELECT
tblEmployee.TFN,
tblEmployee.FirstName,
tblEmployee.MiddleName,
tblEmployee.LastName,
tblEmployee.DOB,
tblEmployee.MailingAddress,
tblEmployee.AddressLine2,
tblEmployee.City,
tblEmployee.fk_StateProvinceID,
tblEmployee.PostalCode,
temp.TotAllow,
temp.TotTax,
temp.TotGross,
temp.TotRESC
FROM
(SELECT
tblEmployee.EmployeeID AS Id
SUM(tblPayment.Allowances) AS TotAllow,
SUM(tblPayment.TaxPayable) AS TotTax,
SUM(tblPayment.GrossPayment) AS TotGross,
(IIF
((SUM(tblSuperPayments.PaymentAmount)) <= (SUM(tblPayment.GrossPayment)*tblSuperRate.SuperRate),
0,
(SUM(tblSuperPayments.PaymentAmount) - (SUM(tblPayment.GrossPayment)*tblSuperRate.SuperRate))
)) As TotRESC
FROM
((tblEmployee
LEFT JOIN tblPayment // any reason for using left join over inner join
ON tblEmployee.EmployeeID = tblPayment.fk_EmployeeID)
LEFT JOIN tblSuperPayments // any reason for using left join over inner join
ON tblEmployee.EmployeeID = tblSuperPayments.fk_EmployeeID)
LEFT JOIN tblSuperRate // any reason for using left join over inner join
ON (tblPayment.PaymentDate <= tblSuperRate.TaxYearEnd) // these two conditions might be returning
AND (tblPayment.PaymentDate >= tblSuperRate.TaxYearStart) //two SuperRate rows because of using equals in both
WHERE
tblEmployee.fk_EmployerID = 1
GROUP BY
tblEmployee.EmployeeID,
tblSuperRate.SuperRate) temp // Does a single employee have more than one superrate why grouping by it?
JOIN tblEmployee ON tblEmployee.EmployeeID=temp.Id;