为什么MySQL命令连接时端口写错也能正常连接？

Question

mysql命令连接mysql服务为什么-P端口写错也能正常连?
感觉非常的迷幻

sh-4.4# mysql -uroot -p -P3307
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3801
Server version: 8.0.29 MySQL Community Server - GPL

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SHOW VARIABLES LIKE 'skip_networking';
Variable_name	Value
skip_networking	OFF

1 row in set (0.00 sec)

mysql> SHOW VARIABLES LIKE 'port';
Variable_name	Value
port	41018

1 row in set (0.00 sec)

mysql>

1 row in set (0.00 sec)

mysql> SHOW VARIABLES LIKE 'port';
Variable_name	Value
port	41018

1 row in set (0.00 sec)

mysql> exit
Bye
sh-4.4# mysql -uroot -p -P999999
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3836
Server version: 8.0.29 MySQL Community Server - GPL

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> ^C
mysql>

Answer 1

看到这个问题挺有意思，我也分别用 Docker 跑了下 MariaDB 和 MySQL 试了试。

结合 @唯一丶 兄弟的说法，还有这个讨论，推测应该是 mysql 命令在不主动使用 -h 参数时，默认值是 localhost，然后就会判定走 SOCKET 的连接方式。

而 SOCKET 连接方式，不会读取 -P/--port 提供的端口号，是直接通过的 my.cnf 里配置的 /var/run/mysqld/mysqld.sock 进行连接。

MySQL

[ok ] mysql -u root -p
[ok ] mysql -u root -p --port 3307
[bad] mysql -u root -p --port 3307 --protocol=TCP

[ok ] mysql -h localhost -u root -p --port 3307
[bad] mysql -h localhost -u root -p --port 3307 --protocol=TCP

[bad] mysql -h 127.0.0.1 -uroot -p --port 3307

# /etc/my.cnf
[mysqld]
socket=/var/run/mysqld/mysqld.sock
[client]
socket=/var/run/mysqld/mysqld.sock

MariaDB

MariaDB 是 MySQL 的一个分支，按理说两者的现象应该是一致的，但是实际测试效果和 MySQL 不太一样。看起来像是默认使用 --protocol=TCP 的方式进行连接。

[ok ] mysql -u root -p
[bad] mysql -u root -p --port 3307
[ok ] mysql -u root -p --port 3307 --protocol=SOCKET

# /etc/mysql/my.cnf
[client-server]
socket = /run/mysqld/mysqld.sock