MySQL 5.5将字符集从utf8升级为utf8mb4

升级原因

MySQL默认的utf8只支持三字节字符，不支持Emoji表情符（四字节），如果有四字节的字符写入会报错。从MySQL 5.5开始，提供了utf8mb4，支持四字节的字符。
许多使用iphone的用户来在填写昵称的时候会加入Emoji表情符，如果MySQL没有使用utf8mb4字符集，这样的昵称信息就无法写入。

一、升级前。

mysql> SHOW VARIABLES LIKE "character_set%";

+--------------------------+--------------------------------------------------------------------+| Variable_name| Value|+--------------------------+--------------------------------------------------------------------+| character_set_client | utf8 || character_set_connection | utf8 || character_set_database | utf8 || character_set_filesystem | binary || character_set_results| utf8 || character_set_server | utf8 || character_set_system | utf8 || character_sets_dir | /home/sdkserver/local/mysql-5.5.43-linux2.6-x86_64/share/charsets/ |+--------------------------+--------------------------------------------------------------------+8 rows in set （0.00 sec）

mysql> SHOW VARIABLES LIKE "collation%";

+----------------------+-----------------+| Variable_name| Value |+----------------------+-----------------+| collation_connection | utf8_general_ci || collation_database | utf8_unicode_ci || collation_server | utf8_unicode_ci |+----------------------+-----------------+3 rows in set （0.00 sec）

二、修改配置文件。

打开MySQL的配置文件，将字符集的配置修改成如下：

[client]default-character-set = utf8mb4[mysql]default-character-set = utf8mb4[mysqld]character-set-client-handshake = FALSEcharacter-set-server = utf8mb4collation-server = utf8mb4_general_ciinit_connect="SET NAMES utf8mb4"

三、升级后。

mysql> SHOW VARIABLES LIKE "character_set%";

+--------------------------+--------------------------------------------------------------------+| 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 || character_sets_dir | /home/nieyong/local/mysql-5.5.43/share/charsets/ |+--------------------------+--------------------------------------------------------------------+8 rows in set （0.00 sec）

mysql> SHOW VARIABLES LIKE "collation%";

+----------------------+--------------------+| Variable_name| Value|+----------------------+--------------------+| collation_connection | utf8mb4_general_ci || collation_database | utf8mb4_general_ci || collation_server | utf8mb4_general_ci |+----------------------+--------------------+3 rows in set （0.00 sec）

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