PHP连接MySQL 8.0连接不上，查看apache日志报错：PHP Warning: PDO::__construct(): Server sent charset (255) unknown to the client，出现这个的原因是MySQL 8.0 字符集改成了默认： utf8mb4，修改mysql 8.0默认字符集为utf8即可

[client]
default-character-set=utf8
[mysql]
default-character-set=utf8
[mysqld]
character-set-server = utf8
collation-server = utf8_general_ci