SELECT substring_index(substring_index(t.delid,‘,‘, b.help_topic_id + 1), ‘,‘, -1)
FROM (SELECT su.* FROM sys_user su ) t
join mysql.help_topic b ON b.help_topic_id < (LENGTH(t.delid) - LENGTH(REPLACE(t.delid, ‘,‘, ‘‘)) + 1)
原文：http://www.cnblogs.com/sg9527/p/7783610.html