Hi guys,
I have a simple model capturing some data:
class datum(Model):
date_time = DateTimeField()
value = FloatField()
Now I want to query averages by month. In SQL (and excuse me for
thinking SQL for a second) that would involve an EXTRACT(MONTH FROM
date_time) AS month coupled with a GROUP BY month along with the average
aggregate.
According to the docs the values() clause is normally used in
combination with annotate() to achieve such grouping but it only works
for raw fields, not derived ones such as "month". I read somewhere that
the "extra" field then takes care of this but my resulting
datum.objects.extra(select={'month': "EXTRACT(month FROM
date_time)"}).values('month').annotate(Avg('value'))
doesn't actually group by month even though it's supposed to, it rather
generates the annotation for every single datum. What's the *right* way
of doing this without resorting to writing raw SQL?
I'm using django 1.1.1 on ubuntu 9.10 64bit if that matters.
Gunther
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