The database landscape in 2026 has two major shifts: PostgreSQL won the relational wars, and the document vs relational debate largely ended with PostgreSQL's JSON support.
PostgreSQL is the default relational database for new projects. It outperforms MySQL on complex queries, has better JSON support (jsonb), better full-text search, and a richer extension ecosystem (pgvector for embeddings, PostGIS for geo, TimescaleDB for time-series). Supabase, Neon, and Railway all host managed PostgreSQL. Neon's serverless branching (instant database clones for feature branches) is a meaningful DX improvement. MySQL still has a strong position in PHP/WordPress ecosystems and at companies that standardized on it years ago, but no strong reason to choose it for new projects.
MongoDB built its reputation on flexible schemas and horizontal scaling. In 2026, the practical use case is narrower: applications with genuinely unpredictable schemas that change frequently, or where document-level atomic operations are important. Many teams that migrated to MongoDB for 'flexibility' found that as products matured, the lack of schema enforcement created more problems than it solved. PostgreSQL's JSONB covers most of the MongoDB use case while adding joins, transactions, and standard SQL.
SQLite is underrated for production. Litestream (continuous replication to S3), LiteFS (distributed SQLite on Fly.io), and Cloudflare D1 (SQLite at the edge) make SQLite viable for applications with read-heavy workloads and modest write volume. Stack Overflow ran on SQL Server for years with 9M queries/day.
For analytics (OLAP): DuckDB (embedded, column-store, blazing fast for local analytics), ClickHouse (distributed, petabyte-scale), BigQuery (serverless, Google ecosystem). Keep OLAP and OLTP separate.