title: append the data to already existing table in pandas using to_sql
body: <p>I have the following data frame</p>
  
  <pre><code>ipdb&gt; csv_data
    country    sale        date  trans_factor
  0   India  403171  12/01/2012             1
  1  Bhutan  394096  12/01/2012             2
  2   Nepal   super  12/01/2012             3
  3  madhya  355883  12/01/2012             4
  4   sudan     man  12/01/2012             5
  </code></pre>
  
  <p>As of now i am using below code to insert data in table, like if table already exists, drop it and create new table</p>
  
  <pre><code>csv_file_path = data_mapping_record.csv_file_path
  original_csv_header = pandas.read_csv(csv_file_path).columns.tolist()
  csv_data = pandas.read_csv(csv_file_path, skiprows=[0], names=original_csv_header, infer_datetime_format=True)
  table_name = data_mapping_record.csv_file_path.split('/')[-1].split('.')[0]
  engine = create_engine(
      'postgresql://username:password@localhost:5432/pandas_data')
  
  # Delete table if already exits
  engine.execute("""DROP TABLE IF EXISTS "%s" """ % (table_name))
  
  # Write the pandas dataframe to database using sqlalchemy and pands.to_sql
  csv_data_frame.to_sql(table_name, engine, chunksize=1000)
  </code></pre>
  
  <p>But  what i need is, without deleting the table, if table already exists just append the data to the already existing one, is there any way in pandas <code>to_sql</code> method ?</p>