Question

I have a log table in my database which holds all user actions. In this table there is a column called ‘money’ which indicates how much money this user had on that day (there is also a ‘timestamp’ column for each log entry)

How can I retrieve data from that table grouped by week or month, aggregated with average value for money?

Answer 1

The easiest way to do this would be to precalculate the week and/or month and store that data into another field. Then the query is as easy as YourTable.objects.values('week', 'year').annotate(Avg('money)).

You should also be able to do this with extra() parameters, but that is sometimes tricky. That would look like

YourTable.objects.extra(select={
     'week': 'some_method_to_calculate_week_from_timestamp(timestamp)'
}).values('week').annotate(Avg('money'))

How you would calculate the week from timestamp in this second case would depend on your DB. If postgres the information you need would be in here: http://www.postgresql.org/docs/8.1/static/functions-datetime.html