mysql中in 做条件匹配 带逗号的字符串 数据异常解决

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在数据库中表doctor中cancer字段存放着以逗号分隔的外键id
select cancer from doctor where id=1;
数据如下

[tr][td]cancer[tr][td]1,2,3

我需要在表cancer_type中匹配刚刚的外键,
于是用FIND_IN_SET函数:
select * from cancer_type c where FIND_IN_SET(c.cancer_id, (select cancer from doctor where id=1) )
数据如下

cancer_id	cancer_name	cancer_prefix
1	肺癌	Lung
2	结直肠癌	Col
3	胃癌	Sto

用in来匹配却不行
select * from cancer_type where cancer_id in (select cancer from doctor where id=1)
数据如下:

cancer_id	cancer_name	cancer_prefix
1	肺癌	Lung