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

def _set_op(self, node):
        """
        Translate a set operator node into SQLQuery.
        :param node: a treebrd node
        :return: a SQLQuery object for the tree rooted at node
        """
        select_block = str(node.attributes)
        from_block = '({left} {operator} ALL {right}) AS {name}'.format(
            left=self.translate(node.left).to_sql(),
            right=self.translate(node.right).to_sql(),
            operator=self._get_sql_operator(node), name=self._get_temp_name(node))
        return self.query(select_block=select_block, from_block=from_block)