How to create group dialogs in PHP?

Question

PHP

Hi all!
I decided to make a system of both group and private dialogues on my website. So far, I have implemented only private ones, that is, communication between two users with each other.
Structure of private dialogs:
dialogs - id, uid_to, uid_from
messages - id, message, from_id, to_id,
dialog

Answer 1

dialogs (id, name)
messages (id, dialog_id, text, user_id)
dialogs_users (dialog_id, user_id)

Answer 2

And with what frequency to update messages from a DB? And is it possible to somehow update only when there is a new message? riot26