Expression for calculate the difference between two field with a same key in a table

[#1]

Goood mornig,

What I do is this:

The field RESIDUO is the difference of the FIELD "IMPORTO FATTURA - IMPORTO SCADENZA".

In case there are two lines in this case for the field "NUMERO FATTURA", you need to either the residual is calculated as "IMPORTO SCADENZA" where field CAUSALE is "FE" less "IMPORTO SCADENZA" where the field is equal to IN.

It 'possible that there are multiple lines for the field "CAUSALE" equal to "IN".

I've Iattached an example of a file.

[#2]

Good morning,

it's possibile to have an expression that allow me to obtain a field in the column called RESIDUO (in the screen shot there's the formula indicated.)

Thanks

Giovanni