How do I know which database to use when developing a web application?

#webdev #backend #architecture #database

I’m building a web app and want to understand how to choose the right database.
What are the main factors to consider when choosing between SQL databases like PostgreSQL/MySQL and NoSQL databases like MongoDB/Firebase?
In which situations should I use each one, and what would be best for a site that includes users, posts, images, and frequently updated content?

Short version:

How do I choose the right database for a web app, and what are the differences between PostgreSQL, MySQL, MongoDB, and Firebase