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mysql utf8mb4字符集：支持emoji表情符号
㈠ 序言
为了应对无线互联网的机遇和挑战、避免 emoji 表情符号带来的问题、
        涉及无线相关的 mysql 数据库建议都提前采用 utf8mb4 字符集
        这必须要作为移动互联网行业的一个技术选型的要点
㈡ 限制
需要 >= mysql 5.5.3版本、从库也必须是5.5的了、低版本不支持这个字符集、复制报错
㈢ 简要步骤
以下是一个未升级到 5.5.3 的配置步骤：
① 备份数据库
        ② 升级 mysql server 到 v5.5.3+
        ③ 修改 database、table和column字符集
[plain]

# for each database:alter database database_name character set = utf8mb4 collate = utf8mb4_unicode_ci;# for each table:alter table table_name convert to character set utf8mb4 collate utf8mb4_unicode_ci;# for each column:alter table table_name change column_name column_name varchar(191) character set utf8mb4 collate utf8mb4_unicode_ci;# (don’t blindly copy-paste this! the exact statement depends on the column type, maximum length, and other properties. the above line is just an example for a `varchar` column.)   
        ④ 修改 my.cnf
[plain] 
[client]  
default-character-set = utf8mb4
[mysql]  
default-character-set = utf8mb4
[mysqld]  
character-set-client-handshake = false  
character-set-server = utf8mb4  
collation-server = utf8mb4_unicode_ci  
init_connect='set names utf8mb4'
⑤ 重启 mysql server、检查字符集
[plain] 
mysql> show variables where variable_name like 'character/_set/_%' or variable_name like 'collation%';  
+--------------------------+--------------------+  
| variable_name            | value              |  
+--------------------------+--------------------+  
| character_set_client     | utf8mb4            |  
| character_set_connection | utf8mb4            |  
| character_set_database   | utf8mb4            |  
| character_set_filesystem | binary             |  
| character_set_results    | utf8mb4            |  
| character_set_server     | utf8mb4            |  
| character_set_system     | utf8               |  
| collation_connection     | utf8mb4_unicode_ci |  
| collation_database       | utf8mb4_unicode_ci |  
| collation_server         | utf8mb4_unicode_ci |  
+--------------------------+--------------------+  
 rows in set (0.00 sec)
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