Calculate Fields

Hi, everybody,

I'm new to SQL, hope you could help me.

I have a table named salary in sql server side, it contains several fields such as housing,overtime, netwage,totalnet gross, tax, factor...etc, the totalnet=netwage+housing+overtime, and gross=totalnet+tax.etc... and tax is calculated from a funcion below:

function taxn(ran:double):double;
var
saSum: Double;
begin
saSum := ran - 1600;
if saSum <=0 then result := 0
else if saSum <= 475 then Result := (saSum-0)/(1 - 0.05)*0.05-0
else if saSum < 1825 then Result := (saSum-25)/(1 - 0.1)*0.1-25
else if saSum < 4375 then Result := (saSum-125)/(1 - 0.15) *0.15-125
else if saSum <= 16375 then Result := (saSum-375)/(1 - 0.2)*0.2-375
else if saSum <= 31375 then Result := (saSum-1375)/(1 - 0.25)*0.25-1375
else if saSum <= 45375 then Result := (saSum-3375)/(1 - 0.3)*0.3-3375
else if saSum <= 58375 then Result := (saSum-6375)/(1 - 0.35)*0.35-6375
else if saSum <= 70375 then Result := (saSum-10375)/(1 - 0.4)*0.4-10375
else if saSum > 70375 then Result := (saSum-15375)/(1 - 0.45)*0.45-15375;
end;

ran=totalnet.

when the table loaded into a DBGrid, it is filled with housing, overtime and netwage, how to calculate other fields and display all in the DBGrid?

I tried to use onCalcFields events as below:

procedure TForm1.ADODataSet1CalcFields(DataSet: TDataSet);
var
totalnet,tax,taxedsalary:extended;
begin

with DataSet do
begin
FieldByName('totalnet').Value :=fieldbyname('housing').Value+fieldbyname('overtime').Value+fieldbyname('netwage').Value;
totalnet := fieldbyname('totalnet').Value;
fieldByName('taxedsalary').Value := roundto(taxbase(totalnet)+0.0001,-2);
tax:=roundto((taxn(totalnet)+0.0001),-2);
fieldbyname('totalgross').Value := totalnet+tax;
fieldbyname('tax').Value := tax;
fieldbyname('taxrate').Value :=floattostr(100*taxraten(totalnet))+'%';
fieldbyname('factor').Value:=factorn(totalnet);
end;
end;

but nothing happened.

Could you shed some lights?

THank you in advance.