title: INSERT if not Exist Mysql
body: <p>I have this table</p>
  
  <pre><code>id     follow_id    follower_id
   1  |       2     |      3
   2  |       2     |      4
   3  |       2     |      5
   4  |       2     |      6
   5  |       3     |      7
   6  |       3     |      8
  </code></pre>
  
  <p>I'd like to skip If i try to insert the "couple" follow_id 2, follower_id 3 without do subquery for the performance</p>
  
  <p>can I do INSERT... ON DUPLICATE KEY UPDATE or something of this?</p>
  
  <p><strong>UPDATE, for symfony user</strong></p>
  
  <p>after answers. i Use Symfony, and for do </p>
  
  <pre><code>UNIQUE INDEX followee_and_follower (follow_id,follower);
  </code></pre>
  
  <p><a href="http://docs.doctrine-project.org/en/2.0.x/reference/annotations-reference.html#uniqueconstraint" rel="nofollow">http://docs.doctrine-project.org/en/2.0.x/reference/annotations-reference.html#uniqueconstraint</a></p>