Messaging system MYSQL, issue with getting latest reply
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I have a table with

message_id, to_id, from_id, message

I made a threaded messaging system. I have 5 people talking to 1 member.

As the member I see

Member 1 says hi, member 2 says hello    ( I want this to say latest reply was hello )

Member 1 says hi, member 3 says hi, member 1 says welcome ( I want this to say welcome )

member 2 says hi (I want this to say hi )

Now, I'm only provided with one of the ID's which is the sessionid of the member1. How would I go about showing scenario 2 where I (member1) have left the latest reply.

I can easily do 

     SELECT * FROM messages WHERE to_id=$session_id ORDER BY message_id DESC LIMIT 1 

but that would only show the INCOMING messages. I need to show the LAST of the incoming AND outgoing messages.

What query would you suggest? :\ Maybe an alteration to the table if there's no efficient way? First time i've ever setup a messaging system, advice is welcome.