mysql 对字符串字段拆分查询

#tag_ids=45,44,43,40,
SELECT 
SUBSTRING_INDEX(tag_ids,",",1),
SUBSTRING_INDEX(SUBSTRING_INDEX(tag_ids,",",2),",",-1),
SUBSTRING_INDEX(SUBSTRING_INDEX(tag_ids,",",3),",",-1),
SUBSTRING_INDEX(SUBSTRING_INDEX(tag_ids,",",4),",",-1),
tag_ids
FROM `ac_achievement` ;