MySQL 5.5 from MySQL 4.1.22 feature request. The query have worked.

DROP TABLE IF EXISTS `node_object`;
CREATE TABLE `node_object` (
`node_id` int(22) NOT NULL default '0',
`class_id` int(22) NOT NULL default '0',
`master_id` int(22) NOT NULL default '0',
`reference_id` int(22) NOT NULL default '0',
PRIMARY KEY (`node_id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;


select o.node_id
from
node_object o
cross join node_object o_6
on o_6.class_id='6'
and o_6.node_id in (o_7.master_id,o_9.master_id)
left join node_object o_7
on o_7.class_id='7'
and o_7.master_id=o_6.node_id
left join node_object o_9
on o_9.class_id='9'
group by o.node_id