mysql拆分逗號一列變多行

需求：

 

SELECT 
DISTINCT substring_index(substring_index(a.value, ',', b.help_topic_id + 1), ',', - 1)
FROM TABLE a
INNER JOIN mysql.help_topic b
    ON b.help_topic_id < (length(a.value) - length(replace(a.value, ',', '')) + 1)