storing averages in a separate data

[Radu Manuel Cirstoiu]

Hi
I'm writing an application(school project) which deals with a portfolio of stocks.
I have a table where I store transactions (stocks being bought or sold).
The Portfolio table would contain the averages of stocks from each transaction.
If you buy 100 stock A at price 3$, and then another 100 stock A at price 4$, then the data would look something like:

portfolio:

share_name volume average_price
---------------------------------
A 200 3.5$

transaction:

share_name volume price
--------------------------
A 100 3$
A 100 4$


Would that make sense for performance (not having to re-compute an user's portfolio over and over again) or would that be a big NO-NO? (I couldn't see how this would violate normalization)

Thanks!