Двойной запрос

 $sql = "SELECT *
    FROM cms_video_category  c1
   JOIN cms_video_category c2
     ON c1.id = c2.parent_id
    ";

SHOW CREATE TABLE cms_video_category \G

CREATE TABLE IF NOT EXISTS `cms_video_category` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `parent_id` INT(11) NOT NULL,
  `ordering` INT(11) NOT NULL DEFAULT '1',
  `NSLeft` INT(11) NOT NULL,
  `NSRight` INT(11) NOT NULL,
  `NSDiffer` VARCHAR(15) NOT NULL,
  `NSIgnore` INT(11) NOT NULL,
  `NSLevel` INT(11) NOT NULL,
  `title` VARCHAR(100) NOT NULL,
  `description` VARCHAR(300) NOT NULL,
  `published` tinyint(1) NOT NULL,
  `showdate` tinyint(1) NOT NULL DEFAULT '1',
  `iconurl` VARCHAR(100) NOT NULL,
  `pubdate` DATE NOT NULL,
  `orderby` VARCHAR(20) NOT NULL DEFAULT 'title',
  `orderto` VARCHAR(4) NOT NULL DEFAULT 'asc',
  `public` tinyint(1) NOT NULL,
  `perpage` INT(11) NOT NULL DEFAULT '15',
  `cssprefix` VARCHAR(20) NOT NULL,
  `nav` tinyint(1) NOT NULL DEFAULT '1',
  `uplimit` INT(11) NOT NULL,
  `maxcols` INT(11) NOT NULL DEFAULT '4',
  `orderform` tinyint(1) NOT NULL DEFAULT '1',
  `showtags` tinyint(1) NOT NULL DEFAULT '1',
  `bbcode` tinyint(1) NOT NULL DEFAULT '1',
  `user_id` INT(11) NOT NULL DEFAULT '1',
  `is_comments` tinyint(1) NOT NULL,
  `seolink` VARCHAR(50) NOT NULL,
  `name` VARCHAR(50) NOT NULL,
  `keywords` VARCHAR(100) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `user_id` (`user_id`),
  KEY `parent_id` (`parent_id`),
  KEY `NSLeft` (`NSLeft`,`NSRight`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1054 ;

SELECT * FROM cms_video_category WHERE id = parent_id

  $sql = "SELECT id
    FROM cms_video_category  c1
   JOIN cms_video_category c2
     ON c1.id = c2.parent_id
     WHERE c1.seolink = '".$link."'
    ";