title: MySQL sum negative and sum of positive values without sub query
body: <p>I have two tables as follows:</p>
  
  <pre><code>tbl_answers : id, (FK)authorID ...
  
  tbl_answer_votes : id, (FK)voterID, (FK)answerID, vote (sInt, only ever -1 or 1) 
  </code></pre>
  
  <p><code>tbl_answers</code> has a one to many relationship with <code>tbl_answer_votes</code> and a vote can be either negative 1 or positive 1. </p>
  
  <p>I need to join <code>tbl_answer_votes</code> on to <code>tbl_answers</code> but produce the sum of all negative votes for that answer and the sum of all positive votes for the answer as two separate columns.</p>
  
  <p>I can do this by sub-querying but as it will be a small part of a larger query and after reading the pitfalls on sub-queries I would like to try and produce those two negative and positive sums from the votes table as efficiently as possible.</p>