How to create a chat conversation list in php and sql?

So I am trying to build a chat system and am currently trying to list the conversations of a user.

This is my sql table:

ID   |  FROM_USER  |  TO_USER  |  MESSAGE      
------------------------------------------------------------
1    |  16         |  29       |  Hey!         
2    |  29         |  18       | Hii..         
3    |  29         |  16       | What's up?

What I’m trying to do is that show the users whom the user 29 (current user) has texted and the users who have messaged 29. How to achieve this? I have tried it using the ‘GROUP BY’ statement and the ‘DISTINCT’ statement but nothing seems to work. How do I achieve this?

Answer

show the users whom the user 29 (current user) has texted and the users who have messaged 29

You can list all users that received messages from user 19 or sent messages to him as follows:

SELECT DISTINCT 
    CASE WHEN from_user = 19 THEN to_user ELSE from_user END as other_user
FROM mytable
WHERE from_user = 19 OR to_user = 19