code: def get_sql(self, with_default_expression=True):
          '''
          Returns an SQL expression describing the field (e.g. for CREATE TABLE).
          :param with_default_expression: If True, adds default value to sql.
              It doesn't affect fields with alias and materialized values.
          '''
          if with_default_expression:
              if self.alias:
                  return '%s ALIAS %s' % (self.db_type, self.alias)
              elif self.materialized:
                  return '%s MATERIALIZED %s' % (self.db_type, self.materialized)
              else:
                  default = self.to_db_string(self.default)
                  return '%s DEFAULT %s' % (self.db_type, default)
          else:
              return self.db_typf get_sql(self, with_default_expression=True):
          '''
          Returns an SQL expression describing the field (e.g. for CREATE TABLE).
          :param with_default_expression: If True, adds default value to sql.
              It doesn't affect fields with alias and materialized values.
          '''
          if with_default_expression:
              if self.alias:
                  return '%s ALIAS %s' % (self.db_type, self.alias)
              elif self.materialized:
                  return '%s MATERIALIZED %s' % (self.db_type, self.materialized)
              else:
                  default = self.to_db_string(self.default)
                  return '%s DEFAULT %s' % (self.db_type, default)
          else:
              return self.db_type
docs: Returns an SQL expression describing the field (e.g. for CREATE TABLE).
          :param with_default_expression: If True, adds default value to sql.
              It doesn't affect fields with alias and materialized values.