Mysql Client to server character set conversion

Mysql The communication request between the client and the server is essentially a string , Of course, this string will be converted into binary data through some character set encoding , Is there only one character set code for the communication between the client and the server ？ As shown below

Server code

Obviously not , The conversion of three character sets is involved in the process of the server processing the request , These three transformations correspond to three system variables respectively, as shown below

• **character_set_client**： The character set used by the server to decode the string requested by the client .

• **character_set_connection**： When the server processes the request, it will character_set_client Convert character set to character_set_connection Character set .

• **character_set_results**： The character set code used when the server returns to the client .

View the character set as follows

###  For space , Directly use fuzzy query to view , The character set is shown below 
mysql> show variables like '%character%';
+--------------------------+-----------------------------------------+
| Variable_name            | Value                                   |
+--------------------------+-----------------------------------------+
| character_set_client     | utf8                                    |
| character_set_connection | utf8                                    |
| character_set_database   | latin1                                  |
| character_set_filesystem | binary                                  |
| character_set_results    | utf8                                    |
| character_set_server     | latin1                                  |
| character_set_system     | utf8                                    |
| character_sets_dir       | /usr/local/mysql-5.7.26/share/charsets/ |
+--------------------------+-----------------------------------------+
8 rows in set (0.00 sec)

Client code

And if the client sends a request, it will encode the string into binary data according to the character set of the operating system , After receiving the request from the server, the client will also decode the binary data into a string according to the character set of the operating system , How to check the character set of the operating system ？

###  stay /etc/locale.conf file  centos8 The default character set is configured as follows 
[[email protected] ~]# cat /etc/locale.conf 
LANG=en_US.UTF-8

The conversion process

The conversion process involves the conversion of several character sets , Steps are as follows

• The client adopts the system character set, and the default is UTF8 Encode the operation database statement , Become binary data , This is limited to mysql -uroot -pxxx Access client , It does not include popular graphical interface clients such as Navicat,DBeaver etc. .

• After the server receives the binary data sent by the client , Through the character set character_set_client Character set decoding , Change to string .

• Use the decoded string character_set_connection Character set encoding , Become binary data for operating the database , If the character set of the database column and character_set_connection Character sets are different , Then you need to convert the character set , Finally get the result data .

• Before returning to the client, you also need to send the result according to character_set_results Encoding .

• The client receives the returned binary data , It also needs to decode according to the system character set , Finally displayed on the client .

Convert the above file into a flowchart , As shown below

Character set modification

The system variables of the server related character set are three , If you want to modify it, you generally need to modify it synchronously in order to ensure that it will not be garbled , Obviously, this is troublesome , Then we can adopt the following two ways , The effect of these two methods is to update the three system variables related to the server code at one time .

set The way

Use combined commands set names Character set name , The command is demonstrated as follows

mysql> show variables like '%character%';
+--------------------------+-----------------------------------------+
| Variable_name            | Value                                   |
+--------------------------+-----------------------------------------+
| character_set_client     | utf8                                    |
| character_set_connection | utf8                                    |
| character_set_database   | latin1                                  |
| character_set_filesystem | binary                                  |
| character_set_results    | utf8                                    |
| character_set_server     | latin1                                  |
| character_set_system     | utf8                                    |
| character_sets_dir       | /usr/local/mysql-5.7.26/share/charsets/ |
+--------------------------+-----------------------------------------+
8 rows in set (0.00 sec)

mysql> set names gbk;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%character%';
+--------------------------+-----------------------------------------+
| Variable_name            | Value                                   |
+--------------------------+-----------------------------------------+
| character_set_client     | gbk                                     |
| character_set_connection | gbk                                     |
| character_set_database   | latin1                                  |
| character_set_filesystem | binary                                  |
| character_set_results    | gbk                                     |
| character_set_server     | latin1                                  |
| character_set_system     | utf8                                    |
| character_sets_dir       | /usr/local/mysql-5.7.26/share/charsets/ |
+--------------------------+-----------------------------------------+
8 rows in set (0.01 sec)

Modify the configuration file

In the default configuration file /etc/my.cnf, Add client startup system configuration parameters

[client]
default-character-set=gbk

Reconnect the client to get the modified character set , Effect and set similar .