记录一次升级zabbix，数据库报错问题。以下是报错内容

The frontend does not match Zabbix database. Current database 
version (mandatory/optional): 3020000/3020000. Required 
mandatory version: 3000000. Contact your system administrator.

最终解决办法如下：

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| zabbix             |
+--------------------+
4 rows in set (0.00 sec)
 
MariaDB [(none)]> use zabbix;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
MariaDB [zabbix]> update dbversion set mandatory=3000000;
Query OK, 1 row affected (0.09 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
MariaDB [zabbix]> flush privileges;
Query OK, 0 rows affected (0.05 sec)
 
MariaDB [zabbix]> use database mysql;
ERROR 1049 (42000): Unknown database 'database'
MariaDB [zabbix]> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
MariaDB [mysql]>