比较操作中使用不同的字符集或排序规则通常会触发此问题，MySQL 8.0 默认 COLLATE 为 utf8mb4_0900_ai_ci 和 对应列 COLLATE 的 utf8mb4_general_ci 不匹配。

> 作者：陈举超

问题现象

MySQL 5.7.34 升级到 8.0.32 后部分查询语句报错如下：

ERROR 1267 (HY000): Illegal mix of collations (utf8mb4_general_ci,IMPLICIT) and (utf8mb4_0900_ai_ci,IMPLICIT) for operation 'find_in_set'

问题原因

比较操作中使用不同的字符集或排序规则通常会触发此问题，MySQL 8.0 默认 COLLATE 为 utf8mb4_0900_ai_ci 和 对应列 COLLATE 的 utf8mb4_general_ci 不匹配。

问题重现过程

创建测试表。

CREATE TABLE `t01` ( `ID` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL, `A_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL, `B_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL, PRIMARY KEY (`ID`) USING BTREE ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci ROW_FORMAT=DYNAMIC; 

执行查询语句。

SELECT AAA.* FROM( SELECT @xxx AS _xxx, ( SELECT @xxx := GROUP_CONCAT( A_CODE ) FROM t01 WHERE FIND_IN_SET( B_CODE, @xxx ) ) AS cxxx FROM t01,( SELECT @xxx := 'xxx') b WHERE @xxx IS NOT NULL) ID,t01 AAA WHERE FIND_IN_SET( AAA.A_CODE, ID._xxx ) order by A_CODE; 

报错。

ERROR 1267 (HY000): Illegal mix of collations (utf8mb4_general_ci,IMPLICIT) and (utf8mb4_0900_ai_ci,IMPLICIT) for operation 'find_in_set'

问题分析

查看默认排序规则。

mysql> show collation like 'utf8mb4_0900_ai_ci'; +--------------------+---------+-----+---------+----------+---------+---------------+ | Collation | Charset | Id | Default | Compiled | Sortlen | Pad_attribute | +--------------------+---------+-----+---------+----------+---------+---------------+ | utf8mb4_0900_ai_ci | utf8mb4 | 255 | Yes | Yes | 0 | NO PAD | +--------------------+---------+-----+---------+----------+---------+---------------+ 1 row in set (0.00 sec) mysql> show collation like 'utf8mb4_general_ci'; +--------------------+---------+----+---------+----------+---------+---------------+ | Collation | Charset | Id | Default | Compiled | Sortlen | Pad_attribute | +--------------------+---------+----+---------+----------+---------+---------------+ | utf8mb4_general_ci | utf8mb4 | 45 | | Yes | 1 | PAD SPACE | +--------------------+---------+----+---------+----------+---------+---------------+ 1 row in set (0.00 sec) mysql> SELECT * FROM INFORMATION_SCHEMA.COLLATIONS WHERE IS_DEFAULT='Yes' and CHARACTER_SET_NAME='utf8mb4'; +--------------------+--------------------+-----+------------+-------------+---------+---------------+ | COLLATION_NAME | CHARACTER_SET_NAME | ID | IS_DEFAULT | IS_COMPILED | SORTLEN | PAD_ATTRIBUTE | +--------------------+--------------------+-----+------------+-------------+---------+---------------+ | utf8mb4_0900_ai_ci | utf8mb4 | 255 | Yes | Yes | 0 | NO PAD | +--------------------+--------------------+-----+------------+-------------+---------+---------------+ 1 row in set (0.00 sec) 

查看相关参数。

mysql> show variables like '%collation%'; +-------------------------------+--------------------+ | Variable_name | Value | +-------------------------------+--------------------+ | collation_connection | utf8mb4_0900_ai_ci | | collation_database | utf8mb4_general_ci | | collation_server | utf8mb4_general_ci | | default_collation_for_utf8mb4 | utf8mb4_0900_ai_ci | +-------------------------------+--------------------+ 4 rows in set (0.00 sec) 其中: mysql> show global variables like '%collation%'; +-------------------------------+--------------------+ | Variable_name | Value | +-------------------------------+--------------------+ | collation_connection | utf8mb4_general_ci | | collation_database | utf8mb4_general_ci | | collation_server | utf8mb4_general_ci | | default_collation_for_utf8mb4 | utf8mb4_0900_ai_ci | +-------------------------------+--------------------+ 4 rows in set (0.00 sec) 

查看配置文件参数。

mysql@CJC-DB-01:/home/mysql$cat /etc/my.cnf ...... [mysqld] collation_server = utf8mb4_general_ci 

可以看到，客户端局部会话变量 collation_connection 的值为 utf8mb4_0900_ai_ci，而全局变量值为 utf8mb4_general_ci，两者不一致。

这是由于服务端在客户端连接时，获取了客户端对字符集和排序规则的缺省设置，也就是 utf8mb4_0900_ai_ci。

解决方案

1. 修改参数
2. 修改表 COLLATE
3. 修改 SQL 语句

1. 修改参数

参数collation_connection 在客户端局部变量值和全局变量值不一致，如何改成一致？官网参考材料

--character-set-client-handshake Command-Line Format:--character-set-client-handshake[={OFF|ON}] Deprecated:8.0.35 Type:Boolean Default Value:ON 

参数说明

• 不忽略客户端发送的字符集信息
• 为了忽略客户端信息并使用默认的服务器字符集
• 使用参数：--skip-character-set-client-handshake

此选项在 MySQL 8.0.35 及更高版本的 MySQL 8.0 中已被弃用。在该版本中，无论何时使用此选项，都会发出警告，并将在未来版本的 MySQL 中删除。

依赖此选项的应用程序应该尽快开始迁移。

添加 my.cnf 参数。

[mysqld] skip-character-set-client-handshake 

重启 MySQL。

mysqladmin -uroot -p****** shutdown mysqld --defaults-file=/etc/my.cnf --user=mysql & 登录 mysql -uroot -p cjc 查看参数，collation_connection 参数值修改成功 mysql> show global variables like '%collation%'; +-------------------------------+--------------------+ | Variable_name | Value | +-------------------------------+--------------------+ | collation_connection | utf8mb4_general_ci | | collation_database | utf8mb4_general_ci | | collation_server | utf8mb4_general_ci | | default_collation_for_utf8mb4 | utf8mb4_0900_ai_ci | +-------------------------------+--------------------+ 4 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 | | default_collation_for_utf8mb4 | utf8mb4_0900_ai_ci | +-------------------------------+--------------------+ 4 rows in set (0.01 sec) 

再次执行，问题解决。

SELECT AAA.* FROM( SELECT @xxx AS _xxx, ( SELECT @xxx := GROUP_CONCAT( A_CODE ) FROM t01 WHERE FIND_IN_SET( B_CODE, @xxx ) ) AS cxxx FROM t01,( SELECT @xxx := 'xxx') b WHERE @xxx IS NOT NULL) ID,t01 AAA WHERE FIND_IN_SET( AAA.A_CODE, ID._xxx ) order by A_CODE; Empty set, 2 warnings (0.00 sec) 

2. 修改表 COLLATE

先改回原参数，查询报错。

SELECT AAA.* FROM( SELECT @xxx AS _xxx, ( SELECT @xxx := GROUP_CONCAT( A_CODE ) FROM t01 WHERE FIND_IN_SET( B_CODE, @xxx ) ) AS cxxx FROM t01,( SELECT @xxx := 'xxx') b WHERE @xxx IS NOT NULL) ID,t01 AAA WHERE FIND_IN_SET( AAA.A_CODE, ID._xxx ) order by A_CODE; ERROR 1267 (HY000): Illegal mix of collations (utf8mb4_general_ci,IMPLICIT) and (utf8mb4_0900_ai_ci,IMPLICIT) for operation 'find_in_set' 

修改表排序规则。

mysql> show create table t01\G; *************************** 1. row *************************** Table: t01 Create Table: CREATE TABLE `t01` ( `ID` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL, `A_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL, `B_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL, PRIMARY KEY (`ID`) USING BTREE ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci ROW_FORMAT=DYNAMIC 1 row in set (0.00 sec) ERROR: No query specified 

修改所有列 COLLATE，实际上只修改 A_CODE、B_CODE 列 COLLATE 也可解决此问题。

ALTER TABLE cjc.t01 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci; ALTER TABLE cjc.t01 MODIFY COLUMN `ID` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL; ALTER TABLE cjc.t01 MODIFY COLUMN `A_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL; ALTER TABLE cjc.t01 MODIFY COLUMN `B_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL; 

再次执行，问题解决。

SELECT AAA.* FROM( SELECT @xxx AS _xxx, ( SELECT @xxx := GROUP_CONCAT( A_CODE ) FROM t01 WHERE FIND_IN_SET( B_CODE, @xxx ) ) AS cxxx FROM t01,( SELECT @xxx := 'xxx') b WHERE @xxx IS NOT NULL) ID,t01 AAA WHERE FIND_IN_SET( AAA.A_CODE, ID._xxx ) order by A_CODE; Empty set, 2 warnings (0.00 sec) 

查看表结构。

mysql> show create table t01\G; *************************** 1. row *************************** Table: t01 Create Table: CREATE TABLE `t01` ( `ID` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL, `A_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL, `B_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL, PRIMARY KEY (`ID`) USING BTREE ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci ROW_FORMAT=DYNAMIC 1 row in set (0.00 sec) 

3. 修改 SQL 语句

将 A_CODE，B_CODE 列的 COLLATE 在 SQL 语句中转换为 utf8mb4_0900_ai_ci。

改写后的SQL如下：

SELECT AAA.* FROM( SELECT @xxx AS _xxx, ( SELECT @xxx := GROUP_CONCAT( A_CODE COLLATE utf8mb4_0900_ai_ci ) FROM t01 WHERE FIND_IN_SET( B_CODE COLLATE utf8mb4_0900_ai_ci, @xxx ) ) AS cxxx FROM t01,( SELECT @xxx := 'xxx') b WHERE @xxx IS NOT NULL) ID,t01 AAA WHERE FIND_IN_SET( AAA.A_CODE COLLATE utf8mb4_0900_ai_ci, ID._xxx ) order by A_CODE; 

总结

比较三种解决方案，每种解决方案适用场景不同，请根据实际情况选择解决方案。

1. 修改参数

   适用于数据库是从 5.7 或更低版本升级到 8.0，并且表数量较多、数据量加大。不适用于批量修改所有表、列字符集和排序规则。

2. 修改表 COLLATE

   适用于修改过程会锁表，数据量越大时间越长，使用于数据量小的场景，建议将所有表、列字符集和排序规则改成 8.0 默认值，后续新增表时不指定字符集和排序规则。

3. 修改 SQL 语句

   适用于临时查询，改SQL影响最小。

更多技术文章，请访问：https://opensource.actionsky.com/

关于 SQLE

SQLE 是一款全方位的 SQL 质量管理平台，覆盖开发至生产环境的 SQL 审核和管理。支持主流的开源、商业、国产数据库，为开发和运维提供流程自动化能力，提升上线效率，提高数据质量。

✨ Github：https://github.com/actiontech/sqle

📚 文档：https://actiontech.github.io/sqle-docs/

💻 官网：https://opensource.actionsky.com/sqle/

👥 微信群：请添加小助手加入 ActionOpenSource

🔗 商业支持：https://www.actionsky.com/sqle