title: Table structure for a conversation messaging system
body: <p>I'm looking to build a messaging system that handles conversation much like how Facebook does it. I'm wondering what the best way to do that would be in regards to table structure. Would I have one table like:</p>
  
  <pre>
  id
  reply_id - the id of the original message that started the conversation
  to_id
  from_id
  subject
  content
  date_sent
  read_status
  </pre>
  
  <p>Or two tables:</p>
  
  <pre>
  table 1 - for the start of new messages
  
  id
  to_id
  from_id
  subject
  content
  date_sent
  read_status
  
  table 2 - when someone replies to a message
  
  id
  message_id
  to_id
  from_id
  subject
  content
  date_sent
  read_status
  </pre>