The behavior is there because you can't limit an aggregate function in
(AFAIK) SQL in that way. It just doesn't make sense--what would this
actually mean?
select sum(price) from product limit 100;
Really, you'd be limiting the number of *rows* of sum returned, which,
unless you're using GROUP, is going to be 1. To do what you want,
you'd need a subselect, which (correct me if I'm wrong,) you'd have to
manually write in SQL. Like so:
select sum(price) from (select price from product order by price desc
limit 100) as q;
(That's postgres; your DB may vary.)
I could be completely off-base here, as I haven't delved very far into
the aggregate code, but from what I can tell, this is the case.
-Jeff
On Mar 3, 11:08 am, Alex Gaynor <alex.gay...@gmail.com> wrote:
> On Tue, Mar 3, 2009 at 8:55 AM, Ross <real...@gmail.com> wrote:
>
> > I have started using aggregation, but it seems to ignore any slicing I
> > do on a QuerySet before calling aggregate. This is what I'm doing:
>
> > Product.objects.order_by("-price")[:100].values("price").aggregate(Max
> > ("price"), Min("price"))
>
> > I want the maximum and minimum price for the products with the top 100
> > largest prices. The aggregate function, however, returns the maximum
> > and minimum price for all Products--it ignores the [:100] slice.
>
> > Is this an improper use of aggregation, or am I doing something wrong
> > with my query?
>
> Before an aggregation is preformed all limits are removed, so you are seeing
> expected behavior. I can't remember why this behavior exists though :/
>
> Alex
>
> --
> "I disapprove of what you say, but I will defend to the death your right to
> say it." --Voltaire
> "The people's good is the highest law."--Cicero
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