I am creating a python CLI app with psql for invoicing.
For sale_invoice_detail table, I have created columns, rate_after_discount
and amount_after_discount. I do the appropriate calculations in my python
code to set/update values in these columns when rate, qty, discount etc are
set/modified.
Now, I shall need the sum of the sub-totals (amount_after_discount of the
above table). Should I save this amount in the sale_invoice table and
ensure that the value gets updated when there is any related change in the
sale_invoice_detail table or is there a better way?