ERROR 1253 (42000): COLLATION 'utf8mb4_bin' is not valid for CHARACTER SET 'utf8'

问题：Moodle系统添加用户时报错，ERROR 1253 (42000): COLLATION 'utf8mb4_bin' is not valid for CHARACTER SET 'utf8'

解决：debug显示出错误信息，需要修改mysql数据表的编码

方法：

debug的信息显示查询mdl_user表时出错，如下

SELECT 'x' FROM mdl_user WHERE LOWER(email) COLLATE utf8mb4_bin = LOWER('student1@qq.com') AND mnethostid = 1 AND id <> -1 LIMIT 0, 1;

错误信息

ERROR 1253 (42000): COLLATION 'utf8mb4_bin' is not valid for CHARACTER SET 'utf8'

显示数据表mdl_user的编码

show create table mdl_user;

修改数据表编码

alter table mdl_user convert to character set utf8mb4;