mysql创建数据库可以用以下语句：

CREATE DATABASE IF NOT EXISTS test_db
DEFAULT CHARACTER SET utf8
DEFAULT COLLATE utf8_chinese_ci;

指定其默认字符集为 utf8，默认校对规则为 utf8_chinese_ci（简体中文，不区分大小写）

但如果要使用字符集utf8mb4，校对规则为 utf8_chinese_ci时就会报错

mysql> CREATE DATABASE IF NOT EXISTS tyfncms default charset utf8mb4 COLLATE utf8_general_ci;
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id:    43
Current database: test

ERROR 1253 (42000): COLLATION 'utf8_general_ci' is not valid for CHARACTER SET 'utf8mb4'

如果要使用utf8mb4，校对规则应设为utf8mb4_unicode_ci;

CREATE DATABASE IF NOT EXISTS test_db 
default charset utf8mb4 
COLLATE utf8mb4_unicode_ci;

如下：

mysql> CREATE DATABASE IF NOT EXISTS test_db default charset utf8mb4 COLLATE utf8mb4_unicode_ci;
Query OK, 1 row affected (0.00 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test_db            |
+--------------------+
8 rows in set (0.00 sec)

mysql> SHOW CREATE DATABASE test_db;
+----------+--------------------------------------+
| Database | Create Database                      |
+----------+--------------------------------------+
| test_db  | CREATE DATABASE `test_db` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci */ |
+----------+--------------------------------------+
1 row in set (0.00 sec)

mysql>