解决 Illegal mix of collations (utf8mb4_unicode_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE)

1.线上BUG报错：

org.springframework.jdbc.UncategorizedSQLException: PreparedStatementCallback; uncategorized SQLException for SQL [select count(*) from player where name=?]; SQL state [HY000]; error code [1267]; Illegal mix of collations (utf8mb4_unicode_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='; nested exception is java.sql.SQLException: Illegal mix of collations (utf8mb4_unicode_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='
        at org.springframework.jdbc.support.SQLStateSQLExceptionTranslator.translate(SQLStateSQLExceptionTranslator.java:124)
        at org.springframework.jdbc.support.SQLErrorCodeSQLExceptionTranslator.translate(SQLErrorCodeSQLExceptionTranslator.java:322)
        at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:604)
        at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:638)
        at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:667)
--

2.解决思路
1)网上搜索下问题，mysql命令测试了emoji表情：

select count(*) from player where name  collate utf8mb4_unicode_ci =  '��';
ERROR 1267 (HY000): Illegal mix of collations (utf8mb4_unicode_ci,EXPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='
;

结果同样报错
2)查看player表：

show create player;
 CREATE TABLE `player` (
  `id` varchar(24) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `name` varchar(20) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci

字段和表都是使用的utf8mb4 格式，支持emoji表情的
3)查看了数据库的字符配置：

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   | utf8            |
| character_set_filesystem | binary          |
| character_set_results    | utf8            |
| character_set_server     | utf8            |
| character_set_system     | utf8            |
| collation_connection     | utf8_general_ci |
| collation_database       | utf8_general_ci |
| collation_server         | utf8_general_ci |
+--------------------------+-----------------+

果然字符集对不上，之前其他服务器数据库字符集都是utf8mb4

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 |
+--------------------------+--------------------+

3.解决办法：
所以需要将这台机子数据库字符集修改为 utf8mb4 格式，线上有项目再跑，等全部停服了再修改

网上类似问题解决借鉴：
https://stackoverflow.com/questions/32511288/illegal-mix-of-collations-utf8mb4-unicode-ci-explicit-and-utf8-general-ci-coe