Question

So here is my stripped table from the messages module of an app I’m writing.

when I run the following command it goes as expected

SELECT * FROM messages WHERE to_user = 1 OR from_user = 1 GROUP
BY from_user

returns

The drama is that I want to have just one instance of 2 | 1 or 1 | 2 , since in my app I’m trying to group the messages based on the username that has sent the message. I tried without the OR clause, but then when 1 send a message to 2 the message does not appear until he gets a reply from 2.
1 and 2 are dynamic from php variables

Answer 1

Since you’re grouping by username, I would select a single valid list of user ID:

SELECT DISTINCT from_user FROM messages WHERE to_user = 1 
UNION
SELECT DISTINCT to_user FROM messages WHERE from_user = 1 

If you don’t mind duplicates, UNION ALL and removing DISTINCT will improve performance.