mysql报错Illegal mix of collations (utf8_general_ci,IMPLICIT) and (utf8mb4_general_ci,COERCIBLE)

测试人员在测试时输入emoji表情时出现报错，查看日志看到是查询一个sql时报错Illegal mix of collations (utf8_general_ci,IMPLICIT) and (utf8mb4_general_ci,COERCIBLE)。
这是数据库编码问题，进入数据库查看数据库的编码。
一、查看当前数据库的编码

mysql> SHOW VARIABLES WHERE Variable_name LIKE 'character_set_%' OR Variable_name LIKE 'collation%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |
| character_set_connection | utf8                       |
| character_set_database   | latin1                     |
| character_set_filesystem | binary                     |
| character_set_results    | utf8                       |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
| collation_connection     | utf8_general_ci            |
| collation_database       | latin1_swedish_ci          |
| collation_server         | latin1_swedish_ci          |
+--------------------------+----------------------------+
11 rows in set (0.01 sec)

可以看到character_set_database，character_set_server ，collation_database，collation_server 的编码都是不支持emoji表情的。mysql utf8 是最多支持3个字节、utf8mb4 最多支持4个字节、emoji表情是四个字节。所以我们要把编码改成utf8mb4。

二、修改配置文件

[mysqld]
character-set-server=utf8mb4
collation-server=utf8mb4_general_ci

修改完配置文件后重启

systemctl restart msqld

三、验证数据库编码是否改正

mysql> show variables where variable_name like "character_set%" or variable_name like "collation%";
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |
| character_set_connection | utf8                       |
| character_set_database   | utf8mb4                    |
| character_set_filesystem | binary                     |
| character_set_results    | utf8                       |
| character_set_server     | utf8mb4                    |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
| collation_connection     | utf8_general_ci            |
| collation_database       | utf8mb4_general_ci         |
| collation_server         | utf8mb4_general_ci         |
+--------------------------+----------------------------+
11 rows in set (0.01 sec)

可以看到数据库编码已经改正了。