code: def left_join(input, **params):
      
      PARAM_COL_RIGHT = 'col.right'
      PARAM_COL_LEFT = 'col.left'
      PARAM_FIELD_JOIN = 'field.join'
  
      right_df = pd.DataFrame.from_records(input[params.get(PARAM_COL_RIGHT)])
      left_df = pd.DataFrame.from_records(input[params.get(PARAM_COL_LEFT)])
      join_on = params.get(PARAM_FIELD_JOIN)
      res = right_df.set_index(join_on, drop=False).join(left_df.set_index(join_on, drop=False), on=[join_on], rsuffix='_right')
      return Converter.df2list(res)
docs: Left join transformation
      :param input:
      :param params:
      :return: