MySQL查看与修改数据库字符集
MySQL查看与修改数据库字符集
- utf8 vs utf8mb3 vs utf8mb4
- 查看字符集和排序规则
- 默认字符集的继承关系
- 修改字符集和排序规则
-
- 修改数据库的默认字符集
- 修改表的字符集和排序规则
utf8 vs utf8mb3 vs utf8mb4
根据MySQL官方文档解释，目前MySQL中的utf8字符集，实际上是utf8mb3字符集，即用3个字节的Unicode编码；而utf8mb4才是真正意义上的4个字节的UTF8编码。
不过在较新的MySQL版本（8.0.32）中，已经只能查询到utf8mb3和utf8mb4两个UTF8编码，而看不到名为utf8的字符集。
SQL > show character set like 'utf8%';
+---------+---------------+--------------------+--------+
| Charset | Description | Default collation | Maxlen |
+---------+---------------+--------------------+--------+
| utf8mb3 | UTF-8 Unicode | utf8mb3_general_ci | 3 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_0900_ai_ci | 4 |
+---------+---------------+--------------------+--------+
https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb3.html
查看字符集和排序规则
查看数据库默认字符集和排序规则：
SQL > select * from information_schema.schemata
where schema_name in ('app_game','app_work','appdb');
+--------------+-------------+----------------------------+------------------------+----------+--------------------+
| CATALOG_NAME | SCHEMA_NAME | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH | DEFAULT_ENCRYPTION |
+--------------+-------------+----------------------------+------------------------+----------+--------------------+
| def | appdb | utf8mb3 | utf8mb3_general_ci | NULL | NO |
| def | app_game | utf8mb3 | utf8mb3_general_ci | NULL | NO |
| def | app_work | utf8mb3 | utf8mb3_general_ci | NULL | NO |
+--------------+-------------+----------------------------+------------------------+----------+--------------------+
查看表的排序规则（通过排序规则可以看出字符集）：
SQL > select table_schema,table_name,engine,table_collation from information_schema.tables
where table_schema in ('app_game','app_work','appdb');
+--------------+------------+--------+--------------------+
| TABLE_SCHEMA | TABLE_NAME | ENGINE | TABLE_COLLATION |
+--------------+------------+--------+--------------------+
| app_game | persons | InnoDB | utf8mb4_0900_ai_ci |
| appdb | temp_seq | InnoDB | utf8mb3_general_ci |
| appdb | test_table | InnoDB | utf8mb3_general_ci |
+--------------+------------+--------+--------------------+
默认字符集的继承关系
查看建库时指定的字符集：
SQL > show variables like 'character_set_server';
+----------------------+---------+
| Variable_name | Value |
+----------------------+---------+
| character_set_server | utf8mb3 |
+----------------------+---------+
SQL > show create database appdb;
+----------+------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+------------------------------------------------------------------------------------------------------+
| appdb | CREATE DATABASE `appdb` /*!40100 DEFAULT CHARACTER SET utf8mb3 */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+------------------------------------------------------------------------------------------------------+
SQL > show create database app_game;
+----------+---------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+---------------------------------------------------------------------------------------------------------+
| app_game | CREATE DATABASE `app_game` /*!40100 DEFAULT CHARACTER SET utf8mb3 */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+---------------------------------------------------------------------------------------------------------+
其中：
- 服务器级别的默认字符集为
utf8mb3； - 数据库
appdb和app_game建库时都未指定字符集，因而沿用了服务器级别的字符集utf8mb3。
查看建表时指定的字符集和排序规则：
SQL > show create table app_game.persons;
+---------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| persons | CREATE TABLE `persons` (
`id` int NOT NULL,
`name` varchar(50) NOT NULL,
`remark` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+---------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.0036 sec)
SQL > show create table appdb.temp_seq;
+----------+-------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+----------+-------------------------------------------------------------------------------------------------------------+
| temp_seq | CREATE TABLE `temp_seq` (
`id` int NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3 |
+----------+-------------------------------------------------------------------------------------------------------------+
其中:
- 数据库
appdb和app_game的默认字符集都是utf8mb3； app_game.persons在建表时指定了字符集utf8mb4，覆盖了数据库级别的默认字符集utf8mb3；appdb.temp_seq在建表时未指定字符集（上面的DEFAULT CHARSET=utf8mb3是MySQL自动补充的），因而沿用了数据库级别的默认字符集utf8mb3。
修改字符集和排序规则
修改数据库的默认字符集
修改数据库的默认字符集和排序规则：
SQL > alter database appdb character set utf8mb4;
Query OK, 1 row affected (0.0038 sec)
SQL > show create database appdb;
+----------+---------------------------------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+---------------------------------------------------------------------------------------------------------------------------------+
| appdb | CREATE DATABASE `appdb` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+---------------------------------------------------------------------------------------------------------------------------------+
创建一张新表，不指定字符集：
SQL > create table appdb.animals (
-> `id` int not null,
-> `name` varchar(30) not null,
-> primary key(`id`)
-> ) engine=InnoDB;
SQL > show create table appdb.animals;
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| animals | CREATE TABLE `animals` (
`id` int NOT NULL,
`name` varchar(30) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
查看appdb中所有表的字符集：
SQL > select table_schema,table_name,table_collation
from information_schema.tables where table_schema='appdb';
+--------------+------------+--------------------+
| TABLE_SCHEMA | TABLE_NAME | TABLE_COLLATION |
+--------------+------------+--------------------+
| appdb | animals | utf8mb4_0900_ai_ci |
| appdb | temp_seq | utf8mb3_general_ci |
| appdb | test_table | utf8mb3_general_ci |
+--------------+------------+--------------------+
其中:
- 在修改数据库字符集之前已有的表，其字符集和排序规则保持不变，即
utf8mb3和utf8mb3_general_ci； - 在修改数据库字符集之后创建的表，如果建表时未指定字符集，其字符集和排序规则为修改后的数据库字符集和排序规则，即
utf8mb4和utf8mb4_0900_ai_ci。
修改表的字符集和排序规则
修改单张表的字符集：
SQL > alter table appdb.temp_seq character set utf8mb4;
Query OK, 0 rows affected (0.0073 sec)
Records: 0 Duplicates: 0 Warnings: 0
SQL > select table_schema,table_name,table_collation
from information_schema.tables where table_schema='appdb';
+--------------+------------+--------------------+
| TABLE_SCHEMA | TABLE_NAME | TABLE_COLLATION |
+--------------+------------+--------------------+
| appdb | animals | utf8mb4_0900_ai_ci |
| appdb | temp_seq | utf8mb4_0900_ai_ci |
| appdb | test_table | utf8mb3_general_ci |
+--------------+------------+--------------------+
修改单张表的字符集和排序规则：
SQL > alter table appdb.temp_seq character set utf8mb4 collate utf8mb4_general_ci;
Query OK, 0 rows affected (0.0051 sec)
Records: 0 Duplicates: 0 Warnings: 0
SQL > select table_schema,table_name,table_collation
from information_schema.tables where table_schema='appdb';
+--------------+------------+--------------------+
| TABLE_SCHEMA | TABLE_NAME | TABLE_COLLATION |
+--------------+------------+--------------------+
| appdb | animals | utf8mb4_0900_ai_ci |
| appdb | temp_seq | utf8mb4_general_ci |
| appdb | test_table | utf8mb3_general_ci |
+--------------+------------+--------------------+
References
[1] https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb3.html
[2] https://blog.csdn.net/Sebastien23/article/details/125124622