Implementation Following?

Question

PHP

Prompt how to implement the following'a mechanism with the notification on new records.
Interested in implementation details at the database level. I use MySQL, since there is no way to use a non-relational DBMS.
The snag arose due to the fact that a user who is subscribed, for example, to comments on a post, is shown a counter of new comments and it is not clear how to decrement or reset the value of this counter when viewing comments.

Answer 1

I can advise here that:
To make the table "user" - "record" - "last view time".
When the user enters the record, the current time is set.
To get the number of new comments, a query is made: "if the date of the comment is greater than the date of the last view." Etc.
The number of new comments from all entries is taken in the same way.