title: How to avoid showing duplicate rows because conditions
body: <p>The problem is where name_1 writes something to name_2 and name_2 writes something to name_1
  there is a duplicate and as one result because I SELECT name_1, name_2 with condition</p>
  <pre><code>SELECT name_1, name_2 
  FROM class_room 
  WHERE (name_1='$userInSystem' AND name_2 &lt;&gt;'$userInSystem') 
      OR (name_1&lt;&gt;'$userInSystem' AND name_2 ='$userInSystem' ) 
  GROUP BY name_1, name_2 
  ORDER BY id DESC
  </code></pre>
  <p>How is it possible to show results with no duplicate rows,</p>
  <p>I only want to know if there is communication between user_1 and user_2</p>