title: Merging similar columns in PostgreSQL
body: <p>I'm working with PostgreSQL. I have two tables, assume for the sake of this problem <code>me</code> has multiple IDs. The first table <code>Table1</code> deals with messages sent:</p>
  
  <pre><code>me | friends | messages_sent
  ----------------------------
  0      1            10
  0      2             7 
  0      3             7          
  0      4             6
  1      1             5
  1      2            12
  ...
  </code></pre>
  
  <p>The second <code>Table2</code> deals with messages received:</p>
  
  <pre><code>me | friends | messages_received
  ----------------------------
   0      4            17
   0      2             7 
   0      1             9          
   0      3             0
   ...
  </code></pre>
  
  <p>How I can get a table like (though, order of friends not important):</p>
  
  <pre><code>    me | friends | messages_total
      ----------------------------
      0      1            19
      0      2            14 
      0      3             7          
      0      4            23
      ...
  </code></pre>
  
  <p>The part I'm pretty stumped on is joining both tables on <code>me</code> while then adding the values of a friend given an equal value for <code>me</code> ... thoughts?</p>