Hi @Nextgen, the marketplace Insights reflects search demand on Udemy today, so that means more students are searching Mongo than Cassandra today. You might also want to consider consulting some outside sources like Stack Overflow or Google Trends to further investigate if one datastore is more popular than the other or trending up or down.
You're on the right track looking at existing courses on either topic since no matter how popular your topic is, you want to make sure your course is differentiated from the competition and able to address the challenges of students trying to master that topic.
Hope this helps!
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