Query for multiple sqllite tables with php

forgive me if question may sound stupid as I'm a begginer with sql lite but i'm looking for simplest sqllite query php solution that will give me full text results from at least three separate sqllite databases. Google seems to give me links to articles without examples and I have to start from somewhere.

I have three databases: domains.db,(url_table,title_table,date_added_table) , extras.db ( same tables as the first db) and admin.db ( url_table, admin_notes_table)

Now i need php query script that will execute query and give me results from domains.db but if there are matches also from extras.db and admin.db

Im trying to just grasp basics of it and looking for starting point where I can at least study and learn the first code.

Thanks in advance.