MySQL8.0.16版本中新增了一个system_user帐户类型，当新增用户并赋予权限时
mysql> create user 'proxysql'@'192.168.20.%' identified with mysql_native_password by 'iD!^^EjU#Yxr5$p';
ERROR 1227 (42000): Access denied; you need (at least one of) the SYSTEM_USER privilege(s) for this operation
# 原因是由于root用户没有SYSTEM_USER权限，把权限加入后即可解决
mysql> grant system_user on *.* to 'root';
Query OK, 0 rows affected (0.00 sec)
