Illegal mix of collations (utf8_unicode_ci,IMPLICIT)and (utf8_general_ci,IMPLICIT) for operation ‘=‘

报错内容

1267 - Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT) for operation '='

执行的sql为：

select f2.* from folder f2 where f2.parent_id in (
  select id from folder where parent_id is null and rel_type='FOLDER' and org_id!='0'
)

原因

由于新生成的查询的结果字符集为utf8_general_ci，而原有表的字符集为utf8_unicode_ci。

解决办法

修改表的字符集为utf8

alter table folder convert to character set utf8;