Translate a relation node into SQLQuery.
        :param node: a treebrd node
        :return: a SQLQuery object for the tree rooted at node

def relation(self, node):
        """
        Translate a relation node into SQLQuery.
        :param node: a treebrd node
        :return: a SQLQuery object for the tree rooted at node
        """
        return self.query(select_block=str(node.attributes),
                          from_block=node.name)