/*      free_result()        */
static VALUE stmt_free_result(VALUE obj)
{
    struct mysql_stmt* s = DATA_PTR(obj);
    check_stmt_closed(obj);
    if (s->res) {
        mysql_free_result(s->res);
        s->res = NULL;
    }
    if (mysql_stmt_free_result(s->stmt))
        mysql_stmt_raise(s->stmt);
    return obj;
}