【MySQL】一次扩展平台引发的字符集调整
公司app（安卓）应用扩展ios平台（安卓客户端已经运行一年），由于ios自带emoji表情字符集，api会出现问题，mysql数据库更换utf8mb4，原字符集utf8。utf8mb4和utf8到底有什么区别呢？原来以往的mysql的utf8一个字符最多3字节，而utf8mb4则扩展到一个字符最多能有4字节，所以能支持更多的字符集。
主要思想导出数据，重新建库插入数据
1.查看当前数据库是否支持utf8mb4（貌似版本低于5.5.3的不能用，没测试）
mysql> show charset like 'utf8mb4';
+---------+---------------+--------------------+--------+
| Charset | Description | Default collation| Maxlen |
+---------+---------------+--------------------+--------+
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |#<--支持utf8mb4字符集
+---------+---------------+--------------------+--------+
1 row in set (0.00 sec) 2.停库方案（无法停库可以锁库只读）
PS：无法提供真实数据，以下只做模拟数据
当前mysql字符集
mysql> show variables like 'character_set%';
+--------------------------+-------------------------------------------+
| Variable_name | Value |
+--------------------------+-------------------------------------------+
| character_set_client | utf8 | #<--客户端字符集
| character_set_connection| utf8 | #<--链接字符集
| character_set_database | utf8 | #<--数据库字符集
| character_set_filesystem| binary |
| character_set_results | utf8 | #<--返回字符集
| character_set_server | utf8 | #<--服务端字符集
| character_set_system | utf8 |
| character_sets_dir | /application/mysql-5.5.32/share/charsets/ |
+--------------------------+-------------------------------------------+
8 rows in set (0.00 sec) 模拟库和表
创建库
mysql> create database app character set utf8 collate utf8_general_ci;
Query OK, 1 row affected (0.00 sec)
mysql> show databases like 'app';
+----------------+
| Database (app) |
+----------------+
| app |
+----------------+
1 row in set (0.00 sec)
mysql> show create database app\G
*************************** 1. row ***************************
Database: app
Create Database: CREATE DATABASE `app` /*!40100 DEFAULT CHARACTER SET utf8 */
1 row in set (0.00 sec) 创建表
随意模拟两张表
mysql> show create table user\G
*************************** 1. row ***************************
Table: user
Create Table: CREATE TABLE `user` (
`uid` int(4) NOT NULL AUTO_INCREMENT,
`name` char(20) NOT NULL,
PRIMARY KEY (`uid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
mysql> show create table userclient\G
*************************** 1. row ***************************
Table: userclient
Create Table: CREATE TABLE `userclient` (
`uid` int(4) NOT NULL AUTO_INCREMENT,
`name` char(20) NOT NULL,
PRIMARY KEY (`uid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec) 模拟数据
mysql> insert into user(name) values('evan'),('cker'),('niuniu');
Query OK, 3 rows affected (0.00 sec)
Records: 3Duplicates: 0Warnings: 0
mysql> insert into userclient(name) values('c_埃文'),('c_瑟可'),('c_×××');
Query OK, 3 rows affected (0.01 sec)
Records: 3Duplicates: 0Warnings: 0 3.导出表结构并修改字符集
# mysqldump -uroot -p --default-character-set=utf8 -d app >/opt/app_utf8.sql --dafault-character-set=utf8 以utf8字符集导出表结构，防止乱码
修改表结构的字符集
# sed -i 's@utf8@utf8mb4@g' /opt/app_utf8.sql 4.确保数据不更新，导出所有数据
# mysqldump -uroot -p --quick --no-create-info --extended-insert --default-character-set=utf8 app >/opt/appdata.sql --quit 用于转存大表使用
--no-create-info 不创建create table语句
--extended-insert 使用多行insert语法，减少io读写，和速度
--default-character-set=utf8 按照原有字符集导出，防止乱码
5.重新建库
mysql> drop database app;
Query OK, 2 rows affected (0.05 sec)
mysql> show databases like 'app';
Empty set (0.00 sec)
mysql> create database app character set=utf8mb4 collate=utf8mb4_unicode_ci;
Query OK, 1 row affected (0.00 sec)
mysql> show create database app\G
*************************** 1. row ***************************
Database: app
Create Database: CREATE DATABASE `app` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci */
1 row in set (0.00 sec)
6.导入表结构和数据
修改客户端字符集和库一致
mysql> set names utf8mb4;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like 'character_set%';
+--------------------------+-------------------------------------------+
| Variable_name | Value |
+--------------------------+-------------------------------------------+
| character_set_client | utf8mb4 |
| character_set_connection | utf8mb4 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8mb4 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /application/mysql-5.5.32/share/charsets/ |
+--------------------------+-------------------------------------------+
8 rows in set (0.00 sec) 导入表结构
mysql> use app; #<--进入库
mysql> source /opt/app_utf8.sql;#<--执行备份的sql文件
mysql> show tables;
+---------------+
| Tables_in_app |
+---------------+
| user |
| userclient |
+---------------+
2 rows in set (0.00 sec)
mysql> show create table user\G
*************************** 1. row ***************************
Table: user
Create Table: CREATE TABLE `user` (
`uid` int(4) NOT NULL AUTO_INCREMENT,
`name` char(20) NOT NULL,
PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 #<--字符集为utf8mb4
1 row in set (0.00 sec)
mysql> show create table userclient\G
*************************** 1. row ***************************
Table: userclient
Create Table: CREATE TABLE `userclient` (
`uid` int(4) NOT NULL AUTO_INCREMENT,
`name` char(20) NOT NULL,
PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec) 导入数据
mysql> source /opt/appdata.sql;
...... 查询数据是否正常
mysql> select * from userclient;
+-----+----------+
| uid | name |
+-----+----------+
| 1 | c_埃文 |
| 2 | c_瑟可 |
| 3 | c_××× |
+-----+----------+
3 rows in set (0.00 sec)
mysql> select * from user;
+-----+--------+
| uid | name |
+-----+--------+
| 1 | evan |
| 2 | cker |
| 3 | niuniu |
+-----+--------+
3 rows in set (0.00 sec)
导入数据乱码错误方法
mysql> set names gbk;
Query OK, 0 rows affected (0.00 sec)
mysql> use app;
Database changed
mysql> select * from userclient;
+-----+--------+
| uid | name |
+-----+--------+
| 1 | c_°￡τ |
| 2 | c_ |
| 3 | c_ |
+-----+--------+
3 rows in set (0.00 sec) 上述原因客户端和库表字符集不一样
mysql> show variables like 'character_set%';
+--------------------------+-------------------------------------------+
| Variable_name | Value |
+--------------------------+-------------------------------------------+
| character_set_client | gbk |
| character_set_connection | gbk |
| character_set_database | utf8mb4 |
| character_set_filesystem | binary |
| character_set_results | gbk |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /application/mysql-5.5.32/share/charsets/ |
+--------------------------+-------------------------------------------+
7.服务端默认字符处理（如非必要可以不用处理，只要保证【客户端，和库表】字符一致即可）
客户端
临时生效 （set names 字符集）
永久生效 更改配置文件my.cnf的模块
default-character-set=字符集 #<--添加这一条语句，无需重启服务即可
服务端
更改配置文件my.cnf的模块
default-character-set=字符集适合5.1及以前版本
character-set-server=字符集适合5.5
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