How to make the subscription logic on the site?

Question

YouTube

Good day!
The question arose, how to implement a subscription system?
There is the following idea:
When you click on the subscribe button for a user, the id and name of the subscriber will be added to the table with the name of the user to whom the subscription will be made.
And when a post is created, a function will be triggered that will iterate over the table and display a new post to those users who were in that table. But then the question is how to add the subscriber's data from the users table to another table?

Answer 1

Try Avidemux

Answer 2

insert into select from