Connect a Deno Deploy app to an external PostgreSQL database

Documented steps

1. Auth: Postgres credentials are stored as Deploy env vars/secrets (dashboard or deno deploy env/database CLI); no separate Deno auth for the DB connection.
2. Link the database: dashboard (hostname/port/user/password with Test Connection) or CLI: deno deploy database link my-db "postgres://user:pass@host:5432/db" then deno deploy database assign my-db --app my-api.
3. Deploy injects standard connection env vars automatically: DATABASE_URL plus PGHOST, PGPORT, PGDATABASE, PGUSER, PGPASSWORD.
4. In code use a client that reads standard env vars with zero config: import { Pool } from "npm:pg"; const pool = new Pool();
5. Query: const result = await pool.query("SELECT * FROM users WHERE id = $1", [123]);
6. TLS: Deploy injects necessary certificates into the default cert store, so encrypted connections work without manual TLS setup.
7. Store DATABASE_URL as a secret (deno deploy env add DATABASE_URL "..." --secret) and use per-context values for dev vs prod databases.
8. Run migrations as a pre-deploy command; it receives DENO_TIMELINE to target the correct timeline's database.
9. Official docs: https://docs.deno.com/deploy/reference/databases/ ; https://docs.deno.com/runtime/reference/cli/deploy/