DataTables???

Hey Everyone...

What I need to do is calculate Backorders when creating invoices?

I have thought of a couple ideas, but I cant seem to get it working right.

Idea 1 -- Just create a field in my SQL table called PAR_INSTOCK, and put a formula in of [(PAR_STCK - PAR_SOLD)]....which only works when I change one of the 2 fields in the formula datatype from Nvarchar to NUMERIC...once I do this the calculation is correct...but then it gives me problems with updating the data, and also searching through the records.

Idea 2 -- Fill a temp datatable, with just PAR_STCK, PAR_SOLD...and then just subtract one column from the other in the datatable. But then I cant figure out how to put the result back into the main datatable??

I'm not sure which way is best to go or how to do it exactly..so any help is appreciated!!