【MySQL】一次扩展平台引发的字符集调整

POOPE

　　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: 3  Duplicates: 0  Warnings: 0
mysql> insert into userclient(name) values('c_埃文'),('c_瑟可'),('c_×××');
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

　　3.导出表结构并修改字符集

[root@oserr ~]# 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

[root@oserr ~]# sed -i 's@utf8@utf8mb4@g' /opt/app_utf8.sql

　　4.确保数据不更新，导出所有数据

[root@oserr ~]# 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[client]模块
　　[client]
　　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[mysqld]模块
　　[mysqld]
　　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