🔗 Using select_merge in Ecto for flexible aggregates

The article explains how PostgreSQL aggregate expressions, combined with Elixir and Ecto, can power flexible query generation. At SwayDM, redemption limits are enforced for members and vendors to prevent abuse, but naïve solutions such as loading all redemption history in memory or executing one query per limit quickly become inefficient. Instead, using Ecto.select_merge/3 allows multiple limits to be evaluated in a single query. This approach improves performance, structures results as maps for easy access, and makes extending the system with new limits straightforward.