SQL becomes much easier when you stop thinking in tables and start thinking in facts that must remain true. A checkout model shows where keys, JOINs, transactions, and indexes actually earn their place.
A working endpoint is not yet a reliable API. The real contract includes validation, errors, retries, idempotency, and a way to evolve without making yesterday’s frontend fail tomorrow.
A frontend request does not jump straight from the browser into your backend. It crosses DNS, encrypted connections, edge infrastructure, application code, and a database before the UI sees a result.