title: to_sql error: Unknown object type numpy.ndarray during describe
body: <p>I am trying to insert a dataframe into a sql table and I get the following error</p>
  
  <p>ProgrammingError: (pyodbc.ProgrammingError) ('Unknown object type numpy.ndarray during describe', 'HY000')</p>
  
  <p>for the following code</p>
  
  <pre><code>merged.to_sql('pmg.cwc.EmSignals1', engine, chunksize=1000, 
             if_exists='replace', 
             index=False, 
              dtype ={'monthenddate': sqlalchemy.types.NVARCHAR(length=20),                                                                                                       
             'lastweekday': sqlalchemy.types.NVARCHAR(length=20),
             'item': sqlalchemy.types.NVARCHAR(length=20),
             'sols': sqlalchemy.types.NVARCHAR(length=20),
             'value': sqlalchemy.types.NVARCHAR(length=20)})
  </code></pre>
  
  <p>This is a .head of the dataframe</p>
  
  <p>monthenddate lastweekday   item   sols     value</p>
  
  <p>0   1999-12-31  1999-12-31  value  2W063W1 -0.870225</p>
  
  <p>1   1999-12-31  1999-12-31  value  W1YBRK4  0.078154</p>
  
  <p>2   1999-12-31  1999-12-31  value  X16W902 -0.072731</p>
  
  <p>3   1999-12-31  1999-12-31  value  2X45X4W  1.278582</p>
  
  <p>4   1999-12-31  1999-12-31  value  23X1XWX  0.293649</p>
  
  <p>I have tried a lot, but cannot figure out the cause of the issue. </p>