PostgreSQL

PostgreSQL (often called Postgres) is a powerful open-source object-relational database with over 35 years of active development, originating at UC Berkeley in 1986. It is widely considered the world's most advanced open-source database — ACID-compliant, standards-conformant, and trusted for data integrity in applications ranging from small web services to enterprise financial systems.

Data types go well beyond standard SQL: primitive types (integer, numeric, text, boolean, date/time), structured types (array, range, composite, UUID), JSON/JSONB with rich indexing and querying, and specialised types for geometric shapes, network addresses, and XML. The native JSONB type with GIN indexing makes Postgres viable as a document store alongside its relational role.

Advanced query capabilities include CTEs (WITH clauses, including recursive), window functions, table partitioning (declarative range/list/hash), foreign data wrappers (FDW) for querying external data sources in SQL, logical replication for selective row-level replication, and parallel query execution across multiple CPU cores.

Extensibility is a core design principle: users can define custom functions, operators, data types, index methods, and procedural languages. PostGIS (geospatial) is the most prominent extension, turning Postgres into the world's leading open-source geospatial database. The ecosystem spans hundreds of packages including pg_trgm (fuzzy text search), timescaledb (time-series), and pgvector (vector embeddings for AI).