title: mysql prepared statements with multiple variables
body: <p>Using one variable doesn't give me an error. with two variables it gives me a syntax error.</p>
  <pre><code>set @a= '...';
  set @b = '...';
  
  PREPARE stm1 FROM 
      'SELECT *
      FROM ?
      WHERE username = ?';
  
  EXECUTE stm1 USING @a, @b;
  </code></pre>
  <pre><code>Error Code: 1064. You have an error in your SQL syntax; 
  check the manual that corresponds to your MySQL server version 
  for the right syntax to use near '?  WHERE username = ?' at line 2
  </code></pre>
  <p>other questions didn't help.</p>
  <p>thanks</p>