CREATE TABLE IF NOT EXISTS `link` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(10) NOT NULL,
  `pid` int(11) NOT NULL,
  `link` text NOT NULL,
  `level` int(11) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 ;

INSERT INTO `link` (`id`, `name`, `pid`, `link`, `level`) VALUES
(1, 'name1', 0, '1', 1),
(2, 'name2', 0, '2', 1),
(3, 'name3', 1, '1,3', 2),
(4, 'name4', 2, '2,4', 2),
(5, 'name5', 3, '1,3,5', 3),
(6, 'name6', 4, '2,4,6', 3),
(7, 'name7', 3, '1,3,7', 3),
(8, 'name8', 4, '2,4,8', 3);

select * from link where id = 1
select * from link where pid = 1 //下一级
select * from link where find_in_set(1, link) //所有下级 包含自己
select * from link where find_in_set(1, link) and level >1 //所有下级 不包含自己
select * from link where find_in_set(1, link) and id <> 1

select * from goods where cid in (select id from link where find_in_set(3, link)) //商品表关联