[Ur] Possible to have products in SQL aggregates?

[Daniel Patterson]

I have a table structure like:

A: aId

ABJoin: refA, refB

B: bId, refA, quantity: float

C: token, refB, quantity: float

The goal is, for a given token, to give a list of all the relevant As,
by joining C with B on refB = bId and then joining B and A through the
ABJoin table. I _want_ to see SUM(C.quantity * B.quantity) - ie the
total number of the specific A that is relevant for the referenced
token, but I'm not able to write that product. (I could if I were just
using SQL)

Is there a way to do this? I'd prefer not to bring everything into
code and then re-implement the join and aggregate...