How to organize an update feed with SQL database?

Question

SQL

Thousands of users post new rows to a common SQL database table with hundreds of common tags.
It is necessary to make sure that any user can see on a certain page of the website all updates on several dozen tags to which he is subscribed.
How to implement it?
As far as I know, this task is more suitable for NoSQL databases like MongoDB. But now I can't change what I'm already using - BaaS Backendless. So I'm looking for a solution for this database.
By the way, if you know any tutorials (Russian / English) on how to implement this in MongoDB, please send it off - I will continue to use this database)
Thank you for your time!

Answer 1

It is necessary to process this in-memory, and to go to the database only if the user has just arrived.