选择其他字段上具有相同值的行

Question

So, i have an entity (i'm using symfony) Participant .

In this entity i have : id account_id conversation_id

account_id is the User object, and conversation_id is the Conversation object, both are foreign keys.

I need to know if, for start, user1 and user2 are in the same conversation. And after i need to know if user1, user2.... userN are in the same conversation.

I don't know how to do that simply with a query ? Thanks !

Answer 1

SELECT
   n.*
FROM
   Participant n JOIN
(
  SELECT 
      t.conversation_id
  FROM
      Participant t
  WHERE 
          t.user_id = 'user1' 
      AND 
          t.conversation_id = (SELECT conversation_id FROM Participant WHERE user_id = 'user2' AND conversation_id = t.conversation_id)
) m on m.conversation_id = n.conversation_id