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

1、只要修改一下表的字符集，如下：

ALTER TABLE users CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;

2、

将比较等式一边进行字符串转换，如改为“CONVERT(b.fullCode USING utf8) COLLATE utf8_unicode_ci”