Every application needs to store its data. A (relational) database is the most common choice in many situations. Like every other component of our software project, a database schema must be managed with a version control system. We will never work without source control for our source code files and we must use the same mindset when dealing with a db.
The database is a critical part of our application. If we deploy version 2.0 of our application against version 1.0 of our database, what do we get? A broken application. And that’s why our database should always be under source control right next to our application code.