You are given several Python backend files to review (treat this as an “OA in code-review format”). The code performs database operations such as SQL INSERTs and SELECT queries. Your task: 1) Write at least 10 code-review comments, each focusing on a different area (security, correctness, data modeling, concurrency, reliability, maintainability, etc.). 2) Identify likely issues such as: - Hard-coded secrets/credentials - Problems in the SQL schema/design - Race conditions or missing transactional safeguards 3) For each issue you raise, propose a concrete fix or improvement (code change, schema change, configuration change, or testing/monitoring addition). Assume you cannot run the code; you must review it from reading only.