# Difference between SQL and NoSQL:
- **SQL (Structured Query Language)**:
  - Uses structured schema and tables.
  - Data is stored in tables with rows and columns.
  - Suitable for structured data with predefined schemas.
  - Supports ACID transactions (Atomicity, Consistency, Isolation, Durability).
- **NoSQL (Not Only SQL)**:
  - NoSQL databases are schema-less or have flexible schema.
  - Data is stored in various formats like key-value pairs, documents, graphs, or wide-column stores.
  - Suited for unstructured or semi-structured data.
  - Scales horizontally and offers high performance for large datasets.

# Middleware and its Use:
- **Middleware**:
  - Middleware is software that acts as a bridge between different systems, components, or layers.
  - In web development, middleware functions intercept incoming HTTP requests and perform various operations before passing them to the next middleware or route handler.
- **Use of Middleware**:
  - Authentication: Verify user identity before accessing protected routes.
  - Logging: Record request details like IP, timestamp, and URL for debugging and analytics.
  - Error Handling: Catch and handle errors to prevent server crashes and provide meaningful responses.
  - Request Processing: Modify or augment incoming requests, such as parsing request bodies or adding headers.
  - Caching: Cache responses to improve performance by serving cached data instead of querying the database repeatedly.

# Use of Express.js:
- **Express.js**:
  - Express.js is a minimalist web application framework for Node.js.
  - It simplifies the process of building web applications and APIs by providing a robust set of features and middleware.
- **Use of Express.js**:
  - Routing: Define routes to handle different HTTP requests and endpoints.
  - Middleware: Easily integrate middleware functions for authentication, logging, and error handling.
  - Templating Engines: Support for popular templating engines like EJS and Handlebars.
  - Error Handling: Built-in error handling middleware for graceful error responses.
  - HTTP Utility Methods: Convenient methods to handle HTTP requests, responses, and headers.