I'll give some context so it makes sense. I'm capturing Customer Ratings for Products in a table (Rating) and want to be able to return a Cumulative Moving Average of the ratings based on time.
A basic example follows taking a rating per day:
02 FEB - Rating: 5 - Cum Avg: 5 03 FEB - Rating: 4 - Cum Avg: (5+4)/2 = 4.5 04 FEB - Rating: 1 - Cum Avg: (5+4+1)/3 = 3.3 05 FEB - Rating: 5 - Cum Avg: (5+4+1+5)/4 = 3.75 Etc...
I'm trying to think of an approach that won't scale horribly.
My current idea is to have a function that is tripped when a row is inserted into the Rating table that works out the Cum Avg based on the previous row for that product
So the fields would be something like:
TABLE: Rating | RatingId | DateTime | ProdId | RatingVal | RatingCnt | CumAvg |
But this seems like a fairly dodgy way to store the data.
What would be the (or any) way to accomplish this? If I was to use the 'trigger' of sorts, how do you go about doing that in SQLAlchemy?
Any and all advice appreciated!