PostgreSQL 19 introduces a significant optimization for data aggregation, allowing the database to aggregate data before performing joins. This change can greatly enhance performance without requiring any alterations to existing code. However, some complex features, like `GROUP BY CUBE`, may not fully benefit from this improvement.

This article explains the optimization rules in DuckDB, focusing on how its advanced optimizer enhances query performance. It details the optimizer's structure, core functions, and how to implement custom optimization rules. A brief overview of 26 built-in optimization rules is also provided.