1、部分项目的MySQL连接时候发现，有时只建了%的账号，可以通过localhost连接，有时候连不上。

[root@centos data]# mysql -h 127.0.0.1 -utest1 -p'AAAA###1188'
Warning: Using a password on the command line interface can be insecure.

2、2种连接方法
执行mysql命令时，-h参数填的是localhost 还是IP, 区别如下
当-h参数为localhost的时候，实际上是使用socket连接的（默认连接方式）

[root@centos wwwlogs]# mysql -hlocalhost -utest1 -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 239
Server version: 5.6.50-log Source distribution

Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.

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> status
--------------
mysql  Ver 14.14 Distrib 5.6.50, for Linux (x86_64) using  EditLine wrapper

Connection id:      239
Current database:   
Current user:       shishi_chancai@localhost
SSL:            Not in use
Current pager:      stdout
Using outfile:      ''
Using delimiter:    ;
Server version:     5.6.50-log Source distribution
Protocol version:   10
Connection:     Localhost via UNIX socket
Server characterset:    utf8mb4
Db     characterset:    utf8mb4
Client characterset:    utf8
Conn.  characterset:    utf8

UNIX socket: /tmp/mysql.sock

Uptime:         20 hours 49 min 0 sec*~~

Threads: 2  Questions: 205630  Slow queries: 0  Opens: 208  Flush tables: 1  Open tables: 201  Queries per second avg: 2.743
--------------

mysql> exit
Bye

当-h参数为IP的时候，实际上是使用TCP连接的

[root@centos wwwlogs]# mysql -h127.0.0.1 -utest1 -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 240
Server version: 5.6.50-log Source distribution

Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.

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> status
--------------
mysql  Ver 14.14 Distrib 5.6.50, for Linux (x86_64) using  EditLine wrapper

Connection id:      240
Current database:   
Current user:       shishi_chancai@localhost
SSL:            Not in use
Current pager:      stdout
Using outfile:      ''
Using delimiter:    ;
Server version:     5.6.50-log Source distribution
Protocol version:   10

Connection: 127.0.0.1 via TCP/IP***

Server characterset:    utf8mb4
Db     characterset:    utf8mb4
Client characterset:    utf8
Conn.  characterset:    utf8
TCP port:       3306
Uptime:         20 hours 49 min 14 sec

Threads: 2  Questions: 205635  Slow queries: 0  Opens: 208  Flush tables: 1  Open tables: 201  Queries per second avg: 2.743
--------------

3、结论

版本 授权用户中的%是否包括localhost
MySQL8.0 包括
MySQL5.7 包括
MySQL5.6 不包括
MySQL5.1 不包括
MariaDB 10.3 不包括

4、备注
MySQL5.6 版本授权中
localhost 包含127.0.0.1 和 localhost
127.0.0.1 包含127.0.0.1 不包含 localhost