PostgreSQL Aggregate and Window Function Tuning

GROUP BY and window functions look declarative — the query says what it wants, and PostgreSQL figures out how to compute it. In practice the planner has strong opinions about how : whether to hash or sort, whether to parallelise, whether to spill memory to disk, whether a matching index changes the plan entirely. Learn to read what the planner picked and why, and aggregate-heavy queries become one of the easiest categories to tune. This article is the fifth in the Complete Guide to PostgreSQL SQ