code: def build_select_fields(self):
          
          field_sql = []
  
          # get the field sql for each table
          for table in self.tables:
              field_sql += table.get_field_sql()
  
          # get the field sql for each join table
          for join_item in self.joins:
              field_sql += join_item.right_table.get_field_sql()
  
          # combine all field sql separated by a comma
          sql = 'SELECT {0}{1} '.format(self.get_distinct_sql(), ', '.join(field_sql))
          return sql
docs: Generates the sql for the SELECT portion of the query
  
          :return: the SELECT portion of the query
          :rtype: str