ClickHouse and PostgreSQL are vastly different databases; ClickHouse excels at analytical queries on large, unchanging datasets (OLAP), while PostgreSQL is a flexible, general-purpose database ideal for transactional operations (OLTP). ClickHouse's columnar storage and "insert now, optimize later" approach allow for significantly faster aggregations but make updates slow. PostgreSQL handles updates efficiently but struggles with massive-scale analytics. Key differences include ClickHouse's superior scalability, materialized views, specialized engines, and robust sharding capabilities, making it a strong choice for analytics-heavy applications, although it's often used in conjunction with a relational database like PostgreSQL for transactional needs.