The NoSQL Hype Train
For years, every bootcamp taught MongoDB (NoSQL) because it's easy to set up. You just throw JSON documents into a collection. No schemas, no migrations. It feels fast, until your data becomes complex.
When to use NoSQL (MongoDB)
Use MongoDB if your data has no fixed structure. For example, storing IoT sensor logs where every device sends different data formats, or a rapid MVP where the data model changes every day.
Why PostgreSQL (SQL) is the King
95% of business applications are deeply relational. A User has many Orders. An Order has many Products. SQL databases enforce strict schemas, ensuring data integrity. If you try to save an order for a user that doesn't exist, Postgres blocks it. MongoDB would blindly save it, leaving you with corrupt 'orphan' data.
Default to PostgreSQL. Modern Postgres handles JSON data almost as well as MongoDB, giving you the best of both worlds.