mysql 不使用存储过程 分割字符串并转成一列

mysql.help_topic 这是使用了这个表的主键，因为它是连续的，不会中断的，也可以换成任意一个相似的表

优化前

SELECT 
SUBSTRING_INDEX(SUBSTRING_INDEX('2016,2017,2018,2019,2020',',',help_topic_id+1),',',-1) AS num 
FROM 
mysql.help_topic 
WHERE 
help_topic_id < LENGTH('2016,2017,2018,2019,2020')-LENGTH(REPLACE('2016,2017,2018,2019,2020',',',''))+1

 sql优化，使用mysql 变量  @type

 优化后

SELECT
SUBSTRING_INDEX(SUBSTRING_INDEX(@type,',',help_topic_id+1),',',-1) AS class_id
FROM
mysql.help_topic ,(select @type:=(select ${type} from organization_info where organization_id=#{organizationId} limit 1)) as init
WHERE
LENGTH(@type)-LENGTH(REPLACE(@type,',',''))+1 >help_topic_id