code: def select_field(col, field_or_fields, filters=None):
      
      fields = _preprocess_field_or_fields(field_or_fields)
  
      if filters is None:
          filters = dict()
  
      wanted = {field: True for field in fields}
  
      if len(fields) == 1:
          header = fields[0]
          data = [doc.get(header) for doc in col.find(filters, wanted)]
          return header, data
      else:
          headers = list(fields)
          data = [[doc.get(header) for header in headers]
                  for doc in col.find(filters, wanted)]
          return headers, data
docs: Select single or multiple fields.
  
      :params field_or_fields: str or list of str
      :returns headers: headers
      :return data: list of row
  
      **中文文档**
  
      - 在选择单列时, 返回的是 str, list.
      - 在选择多列时, 返回的是 str list, list of list.
  
      返回单列或多列的数据。