mysql切分一条数据的一个字段分成若干条数据

select test_id,substring_index(substring_index(a.user_ids,',',b.help_topic_id+1),',',-1) 
from
e_plan_test a
join
mysql.help_topic b
on b.help_topic_id < (length(a.user_ids) - length(replace(a.user_ids,',',''))+1)
order by a.ID;