Comment by Darsh Shukla on "Which Database will you use if you are asked to develop a website like Udemy?"

For user and tutor authentication service Firebase Auth and NoSQL database Firestore.
For the user profile and course's metadata will use PostgreSQL.
For a daily snapshot of the transactions and analytical purpose will use BigQuery because it easily merges with Google Analytics.
For related courses and recommendations will use Redis. Which updates periodically on user preference and course rating.
For videos and course material will use Blob Storage like S3 or GCS.

Search Hashnode