php - Select rows with same value on other field -

so, have entity (i'm using symfony) participant.

in entity have : id account_id conversation_id

account_id user object, , conversation_id conversation object, both foreign keys.

i need know if, start, user1 , user2 in same conversation. , after need know if user1, user2.... usern in same conversation.

i don't know how query ? !

select    n.*    participant n join (   select        t.conversation_id         participant t              t.user_id = 'user1'        ,            t.conversation_id = (select conversation_id participant user_id = 'user2' , conversation_id = t.conversation_id) ) m on m.conversation_id = n.conversation_id