Which database should I use?

Default to PostgreSQL for business data, then add others only when needed:

• PostgreSQL / MySQL (SQL): relationships, transactions, reporting — orders, staff, payroll, invoices
• MongoDB / Firestore (NoSQL): flexible documents, fast prototyping, data without fixed structure
• Redis: caching, sessions, queues, real-time counters
• Vector database (pgvector, Pinecone): AI search over embeddings

Why: most business data is relational — SQL keeps it consistent and easy to report on. Supabase adds auth and APIs on top of Postgres.