title: Compare two tables to find different values in mySQL
body: <p>I have two tables like this :</p>
  
  <p>table 1</p>
  
  <pre><code>|id| comments | class    |
  |1 | bla bla  | positive |
  |2 | bla bla  | negative |
  </code></pre>
  
  <p>table 2</p>
  
  <pre><code>|id| comments | class    |
  |1 | bla bla  | positive |
  |2 | bla bla  | positive |
  </code></pre>
  
  <p>I want to compare the <code>class</code> and store it to variable called <code>tp</code> if <code>class</code> in <code>table 1</code> and <code>table 2</code> are positive.
  <br> If the <code>class</code> in <code>table 1</code> is negative and it is positive in <code>table 2</code> it will be stored in <code>fn</code>.
  <br>I've try but can't make it because I'm newbie. I hope someone can help me for this. Thank you.</p>
  
  <p><br>After that I can use <code>tp</code> and <code>fn</code> in php to do some calculation.</p>