Math Formula Into Oracle Function - oracle

Question

I have this Maths formula which i tried to convert into Oracle function.
This is how it must work, taxableIncome loops through the table,it picks the first line on the table and if it is more than CumulativeAmount,it subtracts CumulativeAmount from taxableIncome and keeps the remainder,it multiplies the CumulativeAmount and Percentage to get a value(x),takes the remainder and go next line in the table and subtract the CumulativeAmount from the remainder.when the remainder is less than the CumulativeAmount,it will apply the 17.5 on the remainder.Later I will sum the (x) values to get a total value. The values are not calculating properly.
CREATE OR REPLACE function CalculateIncomeTax(periodId NVARCHAR2,
employeeId NVARCHAR2,paygroupcode PAYROLL_MASTER.PAY_PAY_GROUP_CODE%type,
taxableIncome NUMBER)
return NUMBER
AS
IncomeTax NUMBER (10,2);
BEGIN
SELECT
coalesce(SUM(
CASE WHEN (taxableIncome > T.TAX_CUMMULATIVE_AMOUNT) THEN (taxableIncome -
T.TAX_CUMMULATIVE_AMOUNT)* (T.TAX_PERCENTAGE/ 100)
ELSE 0.00 END
) ,0)
INTO IncomeTax
FROM TAX_LAW T JOIN PAY_GROUP P ON P.PAY_FORMULA_ID =T.TAX_FORMULA_ID
WHERE P.PAY_CODE = paygroupcode;
return IncomeTax;
end;
/
For example:
taxableIncome= 1000,the function must loop on the first line on the
table CummulativeAmount=261,so 1000-261=739, and 0*739=0,0 is
value(x),
next loop 739>70,739 is the remainder,so 739-70=669, and (5/100)*70
=3.5,3.5 is value(x),
next loop 669>100,669-100=569, (10/100)*100=10,10 is value(x),
now 569 < 2810, so (17.5/100)*569=99.575,99.575 is value(x).
so we sum all x =0+3.5+10+99.575= 113.075
if taxableIncome = 300,300 is greater than 261 in the table so we will use the percentage of 0 on it,but we will get 0.now (300-261) is less than 70 so the percentage of 5 cannot be used on it so the Incometax is 0.But 17.5 will be applied on (300-261) to get 6.825,Total IncomeTax is 6.825.This is the logic behind the calculations.I want to used while statement on calculation it.

Answer 1

CREATE OR REPLACE function CalculateIncomeTax2(taxableIncome NUMBER)
return NUMBER
AS
IncomeTax NUMBER (10,2) := 0;
TaxableRemainder NUMBER := taxableIncome;
BEGIN
for r in (select tax_id, tax_percentage, tax_cummulative_amount
from incometax
order by tax_id)
loop
if TaxableRemainder > r.tax_cummulative_amount then
TaxableRemainder := TaxableRemainder - r.tax_cummulative_amount;
incometax := incometax + (r.tax_cummulative_amount * r.tax_percentage / 100);
else
incometax := incometax + (TaxableRemainder * r.tax_percentage / 100);
exit;
end if;
end loop;
return IncomeTax;
end;
/