Im currently using a portal to relay certain information from my main database, the information that is related between the two are the fields of 'Brand' and 'Part Number'.
The only other fields i have in my portal will be
1. Sale Or Purchase (a drop down list to select either sale or purchase).
Is there any kind of calculation so that when i select either the 'sale' or 'purchase' option in the drop down list that it will either add or subtract the quantity, this way my stock list can keep up to date with the correct quantities?