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;
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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”
https://blog.csdn.net/eddy23513/article/details/80746140?utm_source=blogxgwz1
