Re: [NOVICE] where and how to store calculated data?

I'm not sure exactly what you are asking but I have two thoughts.

   * If you want a value to update automatically, the cleanest way to do 
it it probably to to use a trigger that runs on UPDATE 
(https://www.postgresql.org/docs/9.6/static/sql-createtrigger.html).
   * If you are writing your client in python, psql is very much to 
wrong way to interface with the database. You should be using psycopg2 
(http://initd.org/psycopg/docs/).
                  -Ed

On 7/5/2017 7:20 AM, Rounak Jain wrote:
> 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?