MySQL连接方式
关于MySQL的连接问题一直是一个最常见、最普遍问题，同时也是最容易被大家忽略的问题。下面就MySQL的连接方式，简单做一下自己的总结：
一、Socket连接方式
前提条件：只能在MySQL客户端和数据库实例在一台服务器上才可以使用。
mysql默认是以socket的方式登陆的。
localhost使用的也是该方式进行登陆的，localhost方式不通过网络传输，不受网络防火墙和网卡相关的限制。
socket方式制定，使用 -S 选项指定使用的socket。
- 默认方式
# mysql -uroot -p123456 - localhost方式
# mysql -uroot -p123456 -hlocalhost - socket方式
# mysql -uroot -p123456 -S /tmp/mysql.sock
3种方式的结果相同如下（可以自行测试）：
[root@node1 ~]# mysql -uroot -p123456
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.6.30-76.3-25.16-log Percona XtraDB Cluster binary (GPL) 5.6.30-25.16, Revision aa929cb, wsrep_25.16
Copyright (c) 2009-2016 Percona LLC and/or its affiliates
Copyright (c) 2000, 2016, 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.
(product)root@localhost [(none)]> \s
--------------
mysql Ver 14.14 Distrib 5.6.30-76.3, for Linux (x86_64) using 6.0
Connection id: 5
Current database:
Current user: root@localhost <------------ 当前连接用户和方式
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.6.30-76.3-25.16-log Percona XtraDB Cluster binary (GPL) 5.6.30-25.16, Revision aa929cb, wsrep_25.16
Protocol version: 10
Connection: Localhost via UNIX socket <-------------- socket方式连接
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /tmp/mysql.sock <----------- 使用的socket套接字
Uptime: 34 min 43 sec
Threads: 3 Questions: 12 Slow queries: 0 Opens: 70 Flush tables: 1 Open tables: 63 Queries per second avg: 0.005
--------------
(product)root@localhost [(none)]> 注意：在使用socket方式时，为了防止所有用户都可以删除socket，可以对 /tmp 目录设置粘着位。这样只有用户本身和root用户才有权限删除改socket文件。
# chmod +t /tmp
# ls -ld /tmp
二、TCP/IP连接方式
mysql在登陆时，指定-h参数选项时，会采用tcp/ip方式进行连接。
127.0.0.1 默认也是采用该方式，通过网卡传输，依赖网卡，并受到网络防火墙和网卡相关的限制。
如：# mysql -uroot -p123456 -h127.0.0.1 -P3308
(product)root@localhost [(none)]> select host,user from mysql.user;
+-----------+-------------+
| host | user |
+-----------+-------------+
| % | anemometer |
| % | pxc-monitor |
| % | sbtest |
| % | wujj |
| 127.0.0.1 | root | <----------- 必须有127.0.0.1的IP地址
| localhost | root |
| localhost | sst |
+-----------+-------------+
7 rows in set (0.02 sec)
(product)root@localhost [(none)]>
[root@node1 ~]# mysql -uroot -p123456 -h127.0.0.1 -P3308
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 5.6.30-76.3-25.16-log Percona XtraDB Cluster binary (GPL) 5.6.30-25.16, Revision aa929cb, wsrep_25.16
Copyright (c) 2009-2016 Percona LLC and/or its affiliates
Copyright (c) 2000, 2016, 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.
(product)root@127.0.0.1 [(none)]> \s
--------------
mysql Ver 14.14 Distrib 5.6.30-76.3, for Linux (x86_64) using 6.0
Connection id: 8
Current database:
Current user: root@localhost <------------ 当前连接用户和方式
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.6.30-76.3-25.16-log Percona XtraDB Cluster binary (GPL) 5.6.30-25.16, Revision aa929cb, wsrep_25.16
Protocol version: 10
Connection: 127.0.0.1 via TCP/IP <-----------TCP/IP方式连接
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
TCP port: 3308
Uptime: 50 min 39 sec
Threads: 3 Questions: 28 Slow queries: 0 Opens: 70 Flush tables: 1 Open tables: 63 Queries per second avg: 0.009
--------------
(product)root@127.0.0.1 [(none)]> 注意：MySQL 登陆时，同时指定-h和-S(套接字)， MySQL 会默认使用tcp/ip的方式连接。因此随便指定一个socket文件都可以登陆。
三、自定义连接方式参数
[root@node1 ~]# mysql --help|grep protocol
-C, --compress Use compression in server/client protocol.
--protocol=name The protocol to use for connection (tcp, socket, pipe,
(pre-4.1.1) protocol.
[root@node1 ~]# 可以发现默认有3个选项：tcp，socket和pipe（pipe就不说了，有兴趣的可以自己研究）
四、常用检查命令
shell> mysqladmin version
shell> mysqladmin variables
shell> mysqladmin -h hostname version variables
shell> mysqladmin -h hostname –port=3306 version
shell> mysqladmin -h host_ip version
shell> mysqladmin –protocol=SOCKET –socket=/tmp/mysql.sock version
链接地址：
http://dev.mysql.com/doc/refman/5.6/en/can-not-connect-to-server.html