MySQL character sets and comparison rules

Since the need to transmit the encoded string communication between client and server MySQL, it will inevitably produce transcoding

character set

MySQL, utf8is utf8mb3, only 1 to 3 bytes represent characters
utf-8md4using 1 to 4 bytes characters

Related parameters

MySQL server has the following parameters related to the coded
character set parameters:
character_set_server server-level character set of
character_set_databasethe current character set of the database (if no USE select the database, the server-level view of the character set) read-only, can not be changed by modifying the current database parameter
character set conversion parameters:
character_set_client the server that the client sends a request for the character set, the request is decoded to form the character set, content acquisition request for
character_set_connectionthe character set used when the internal server processes the request, the server will be the client request is encoded in the form of the character set (if the character set of the data processing will be different then a conversion)
character_set_resultsthe results returned by the server will be encoded in the form of the character set returned to the client

View command

MySQL supports many character sets, you can view all character sets supported by the following command

SHOW CHARACTER SET;
SHOW CHARSET;

Which Default collationis the default character set of this comparison rule, Maxlenis this character set maximum number of bytes needed a character

View other parameters

SHOW VARIABLES LIKE 'character_set_server';
SHOW VARIABLES LIKE 'character_set_database';
SHOW VARIABLES LIKE 'character_set_client';
SHOW VARIABLES LIKE 'character_set_connection';
SHOW VARIABLES LIKE 'character_set_results';

Set command

Character Set Parameters

Server level:

SET character_set_server 字符集名;

Database level:

CREATE DATABASE 数据库名
CHARACTER SET 字符集名称;

ALTER DATABASE 数据库名
CHARACTER SET 字符集名称;

Table level

CREATE TABLE 表名 (列的信息)
CHARACTER SET 字符集名称;

ALTER TABLE 表名
CHARACTER SET 字符集名称;

Column level

CREATE TABLE 表名(列名 字符串类型 CHARACTER SET 字符集名称);

ALTER TABLE 表名 MODIFY 列名 字符串类型 CHARACTER SET 字符集名称 ;

Set the character set conversion parameters

In order to facilitate the general three parameters will be set to the same character set
, use the following command can be set three parameters simultaneously

SET NAMES 字符集名;

Of course, you can set separately

SET character_set_client = 字符集名;
SET character_set_connection = 字符集名;
SET character_set_results = 字符集名;

Comparison rules

Comparative collation rules is sometimes referred to, for comparing the size of the character string predetermined in the order of
the same characters may have various comparison rule

Naming Rules

Each character set may correspond to a variety of comparison rules, these rules naming rules to compare

Comparison rules names that begin with the corresponding character set name
Mainly for the middle portion represents what language
Suffixes are the following:

Full name suffix meaning

`_ai`	accent insensitive	No accent
`_as`	accent sensitive	Accent
`_ci`	case insensitive	not case sensitive
`_cs`	case sensitive	Case sensitive
`_bin`	binary	Compare binary mode

Example:
utf8_spanish_ciexpressed in Spanish comparison is not case sensitive

Related parameters

collation_serverServer-level comparison rules
collation_databasecomparison of the current rules of the database (if no USE select the database, look at the server level comparison rules) read-only, can not be changed by modifying the parameters of the current database

View command

The comparison rules list them all more, you can filter based on the corresponding character set

SHOW COLLATION;
SHOW COLLATION LIKE 'utf8\_%';

Which Charsetindicates that the corresponding character set, Defaultindicates whether the default comparison rules

Set command

Set more rule parameters

Server level:

SET collation_server 比较规则名;

Database level:

CREATE DATABASE 数据库名
COLLATE 比较规则名称;

ALTER DATABASE 数据库名
COLLATE 比较规则名称;

Table level

CREATE TABLE 表名 (列的信息)
COLLATE 比较规则名称;

ALTER TABLE 表名
COLLATE 比较规则名称;

Column level

CREATE TABLE 表名(列名 字符串类型 COLLATE 比较规则名称);

ALTER TABLE 表名 MODIFY 列名 字符串类型 COLLATE 比较规则名称 ;

to sum up

When only modify the character set or a level of comparison rules, the same rules or the level of the corresponding comparator will also change the character set to the corresponding (default)
when creating a database if you do not specify the character set and comparison rules, the default use server-level parameter
does not specify the character set and comparison rules when creating a table, the default parameters using the database where the table
is created does not specify the character set and comparison rules when a column, use the column where the table of default parameters