sql - Build a Query to get the informations from a specific user -

i'm building chat 3 tables.

conversation, conversation_reply , user

conversation columns

1. id
2. user_one
3. user_two

conversation_reply columns

1. id
2. user_id
3. conversation.id
4. reply

user columns

1. id
2. username

i build list name users chating specific user.

example, id 711, , talking 3 persons, username 3 persons.

i'm having issues building query because user_one , user_two relative, id receiver can inserted user_one, or user_two. depends on user starts chatting first.

how can build query that?

thanks.

depending on rdbms can check if/else, case/when syntax. based on write statement:

select if (user_one=711) user_two else user_one conversation user_one=711 or user_two=711 

this pseudocode, idea should clear.