Writing SELECT , INSERT , UPDATE , and DELETE queries is not the difficult part of a CRUD API. The difficulty begins when every route starts handling SQL, input validation, HTTP status codes, and error formatting at the same time. That version may work for five endpoints. It becomes unpleasant when you add authentication, pagination, related tables, or a second developer. In this tutorial, we will build a Node.js REST API with Express and MySQL while keeping each responsibility in a p...