How to create alert for mobile app (PHP + mySQL + Android studio )?

Question

PHP

What is: a
mobile application on android studio that communicates via json with a database on mysql.
What is required:
So that when data enters the database, push notifications come to the mobile application.
What is the question:
How will the mobile application understand that a new entry has appeared in the mysql database table and it's time to display a notification? do a service in a mobile application that constantly makes queries to the database or are there other options?

Answer 1

gcm works for Android, iOS and Chrome