Translate a relational algebra string into a SQL string.

        :param instring: a relational algebra string to translate
        :param schema: a mapping of relation names to their attributes
        :param use_bag_semantics: flag for using relational algebra bag semantics
        :return: a SQL translation string

def to_sql(self, instring, schema, use_bag_semantics=False):
        """
        Translate a relational algebra string into a SQL string.

        :param instring: a relational algebra string to translate
        :param schema: a mapping of relation names to their attributes
        :param use_bag_semantics: flag for using relational algebra bag semantics
        :return: a SQL translation string
        """
        root_list = self.to_syntax_tree(instring, schema)
        return sql_translator.translate(root_list, use_bag_semantics)