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` ;