select_expr ::= select param_start conditions param_stop expression

def theta_join(self):
        """
        select_expr ::= select param_start conditions param_stop expression
        """
        long = self.parametrize(self.syntax.theta_join_op, self.conditions)
        short = self.parametrize(self.syntax.join_op, self.conditions).\
            setParseAction(self.theta_parse_action)
        return long ^ short