MySQL系统表help_topic的使用

参考https://www.jb51.net/article/231782.htm

SELECT 
 substring_index(substring_index('1,2,3,4',',', b.help_topic_id + 1), ',', -1) result
FROM 
 mysql.help_topic b
where 
 b.help_topic_id <  (LENGTH('1,2,3,4') - LENGTH(REPLACE('1,2,3,4', ',', '')) + 1);

例子：