title: Insert statement that checks for duplicate before insert
body: <p>I need to make a insert but only if similar record don't exists<br>
  for example:  </p>
  
  <blockquote>
    <p>INSERT INTO requests ('user_id','subject','text','time') VALUES (56,'test','test 1234',6516516)</p>
  </blockquote>
  
  <p>but to check if there are same 'subject' and 'text' in another record to:  </p>
  
  <ol>
  <li>not insert anything</li>
  <li>update 'time' and 'user_id'</li>
  </ol>
  
  <p>I need sql for both cases because I'm no sure at this moment what I'm going to use.<br>
  Thanks in advance!</p>