ดึงข้อมูลที่คั่นด้วย คอมม่า(,) แล้วนับจำนวน ทำยังไงครับ

CREATE TABLE tally(n INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
INSERT INTO tally (n)
SELECT 
	NULL
FROM 
	(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
	,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
;

DROP TABLE IF EXISTS `content`;
CREATE TABLE IF NOT EXISTS `content` (
  `id` int(5) NOT NULL AUTO_INCREMENT,
  `chub` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `id` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=latin1;

INSERT INTO `content` (`id`, `chub`) VALUES
	(1, '8,10'),
	(2, '23'),
	(3, NULL),
	(4, '8'),
	(5, '8,10'),
	(6, '10,11');

SELECT 
	`tag`, 
	COUNT(*) AS `num_rows`
FROM
	(
  		SELECT 
		  	c.`id`, 
			SUBSTRING_INDEX(SUBSTRING_INDEX(c.`chub`, ',', n.`n`), ',', -1) AS `tag`
    	FROM 
		 	`content` c 
		CROSS JOIN 
			tally `n`
   	WHERE 
			n.`n` <= 1 + (CHAR_LENGTH(c.`chub`) - CHAR_LENGTH(REPLACE(c.`chub`, ',', '')))
	) q
WHERE 
	CHAR_LENGTH(`tag`) > 0
GROUP BY 
	`tag`
ORDER BY 
	CONVERT(`tag`, SIGNED INTEGER) ASC;