title: mysql_num_rows give unexpected result
body: <p>I've got the following function:</p>
  
  <pre><code>public function already_tweeted($tweet){
          return mysql_num_rows(mysql_query("SELECT * FROM `retweeted` WHERE `tweet`='$tweet'"));
      }
  </code></pre>
  
  <p>Pretty straightforward. It checks whether a tweet already exists in the database.</p>
  
  <p>The table had the following records:</p>
  
  <pre><code>id  user    tweet
  3       You should retweet this too
  2       Retweet this
  </code></pre>
  
  <p>(user is empty for now)</p>
  
  <p>This code:</p>
  
  <pre><code>$db_reader = new database_reader;
  $already_tweeted = $db_reader-&gt;already_tweeted($tweet);
  print $tweet . ". Already: ";
  var_dump((bool) $already_tweeted);
  print "&lt;br&gt;";
  </code></pre>
  
  <p>Gives the following output:</p>
  
  <pre><code>You should retweet this too. Already: bool(false) 
  Retweet this. Already: bool(true) 
  </code></pre>
  
  <p>I'm pretty much stuck here.
  When I run SELECT * FROM <code>retweeted</code> WHERE <code>tweet</code>='You should retweet this too' in phpmyadmin I get 1 row back.</p>