I would always lean on the database to perform simple sums and aggregations unless I was really concerned about turning the database into a performance bottlene

I would always lean on the database to perform simple sums and aggregations unless I was really concerned about turning the database into a performance bottleneck. If you need to add simple logic above and beyond this, stored procedures aren't sexy but they can be a good compromise that avoids shipping data around and re-implementing SQL in your application server.