title: pandas DataFrame.to_sql and nan values
body: <p>I am trying to use pandas DataFrame.to_sql to insert values in a table of my Postgres database. I have some nan values in a column of integers that does not belong to any constraint. </p>
  
  <p>I get the following error : </p>
  
  <pre><code>sqlalchemy.exc.DataError: (DataError) integer out of range
  </code></pre>
  
  <p>When I substitute nan values with zéros, insertion happens as wanted, so it is really nan values that are to blame for my error.</p>
  
  <p>I have tried converting nan values to None and to np.nan , but I get the same error.
  So the question is: what nan format do I need so that pd.to_sql handles it correctly?</p>
  
  <p>My restrictions are : python 2.7 pandas 0.14.1 , sqlalchemy 0.9.8 , Postgres 9.2</p>