select * from tag t where t.tag like ‘%a%c%’;

楼上有缺陷，会查出 abc,b,d

多个like就用and连接多个like嘛

严谨的SQL写法来了

with cte as
(
select 1 as id,'a,b,c' as tag union all
select 2 as id,'a,c,d' as tag union all
select 3 as id,'a,d,e' as tag union all
select 4 as id,'c,d,e' as tag union all
select 5 as id,'a' as tag 
)

select * from cte
where id in
(
	select id from (
		SELECT id,
		SUBSTRING_INDEX(SUBSTRING_INDEX(tag,',',help_topic_id+1),',',-1) AS num
		FROM
		mysql.help_topic ,cte
		WHERE
		help_topic_id < LENGTH(tag)-LENGTH(REPLACE(tag,',',''))+1
	) as t
	where num ='a' or num = 'c'
	group by id
	having count(*) >=2
)

结果
id tag
1 a,b,c
2 a,c,d