title: SQL - Hard time building a "complex" request
body: <p>I've got three tables :</p>
  
  <ul>
  <li><code>conversations</code> (contains private conversations)</li>
  <li><code>conversations-members</code> - structure : <code>convId | userId</code> (contains all ids of members participating to a conversation so multiple people can talk together. One user participating to a conversation equals one row)</li>
  <li><code>users</code> (users table, classic)</li>
  </ul>
  
  
  
  <p>What I am trying to do is : </p>
  
  <p>Users have friends. So, the user browsing my application can open a conversation from his friends' ids.</p>
  
  <p>So, first, I want to look up in <code>conversations-members</code> if there is an existing conversation ONLY between user's Id and his friend's Id and then, pick up the conversation id in <code>conversations</code> table that <code>conversations-members</code> gave me.</p>
  
  <p>Is it possible to do this in one request? If I have to do two requests, I don't even know how to build the first one (<code>find the rows that contain user's Id and friend's Id that have conversation Id in common)</code>.</p>
  
  <p>My first idea was to make a single <code>conversations</code> table which would also contain member's Id in the form of a string like "55,105,85,22" and then parse it to get an array, but I think the way I want to do it gives me more options and could be simpler if I manage to handle the SQL requests I need.</p>