Reaching for something like SUM(vals) or AVG(vals) is a common habit when using PostgreSQL. These aggregate functions offer users an easy, efficient way to compute results from a set of inputs. How do they work? What makes them different than a function? How do we make one? What kinds of other uses exist? We'll explore creating some basic ones using SQL, then create an extension that defines aggregates in Rust using pgx 0.3.0's new aggregate support.
