title: Pandas to_sql Trying to Index Nullable Column
body: <p>I want to set up a job that dumps data into a SQL table every day, overwriting the existing data. </p>
  
  <pre><code>df.to_sql(table_name, engine, schema='dbo', 
            index=True, index_label='IdColumn', 
            if_exists='replace')
  </code></pre>
  
  <p>However behind the scenes SQLAlchemy is trying to create the table with IdColumn VARCHAR(max), and being nullable. So SQL throws an error when it tries to create the index.</p>
  
  <p>It's pretty trivial to truncate the table before I write the data to it, but I feel like there should be a more elegant solution to this problem.</p>