Can you run a database on an Android phone?

Short answer

Yes. Two engines run on the device itself — SQLite/Room and an embedded PostgreSQL 18 server — so you create tables, run SQL, browse data and design ER diagrams entirely offline, with no desktop and no cloud host. Nine more (Neon, Supabase, PlanetScale, MongoDB Atlas, self-hosted MongoDB, Turso, Redis, Upstash, Firestore) are remote services you connect to, and those need a network on Android 9 or newer, with backups and data masking built in.