You’ve probably heard that data is a big deal. By some measures, 90% of the world’s data has been generated in just the past two years! From a stored credit card number on an e-commerce site to the timestamp when you hit pause on Netflix, modern web applications collect a lot of data. For that data to be useful, it has to be organized and stored somewhere.

The back-ends of modern web applications include some sort of database, often more than one. Databases are collections of information. There are many different databases, but we can divide them into two types: relational databases and non-relational databases (also known as NoSQL databases). Whereas relational databases store information in tables with columns and rows, non-relational databases might use other systems such as key-value pairs or a document storage model. SQL, Structured Query Language, is a programming language for accessing and changing data stored in relational databases. Popular relational databases include MySQL and PostgreSQL while popular NoSQL databases include MongoDB and Redis.

In addition to the database itself, the back-end needs a way to programmatically access, change, and analyze the data stored there.