Let’s say you have an application developed in Node.js (or any other platform). This application connects to a MongoDB database (NoSQL) to store ratings on books (number of stars given and a comment). Let’s also say that you have another application developed in Java (or Python, C#, TypeScript… anything). This application connects to a MariaDB database (SQL, relational) to manage a catalog of books (title, year of publishing, number of pages).

You are asked to create a report that shows the title and rating information for each book. Notice that the MongoDB database doesn’t contain the title of the books, and the relational database doesn’t contain the ratings. We need to mix data created by a NoSQL application with data created by a SQL application.