在测试备份还原时，利用XtraBackup还原数据库后，昆山软件开发，建设一个测试账号时碰着了下面错误： 

mysql> grant all on house.* to test@'192.168.%' identified by 'test1249';

ERROR 3009 (HY000): Column count of mysql.user is wrong. Expected 45, found 43. Created with MySQL 50620, now running 50721. Please use mysql_upgrade to fix this error.

mysql>

因为备份的数据库版本为MySQL 5.6.20，方针数据库的MySQL版本为5.7.21，劳务派遣管理系统，因为两个数据库版本纷歧致，在还原事后，昆山软件开发，健忘进级数据库（还原后没有利用mysql_upgrade进级数据布局）。其实从错误信息也能看出一二，需要执行mysql_upgrade呼吁会查抄所有数据库中的所有表与当前版本的MySQL处事器是否不兼容。 mysql_upgrade还会进级系统表，以便你可以利用一些新特性或成果。

# mysql_upgrade -u root -p
Enter password: 
Checking if update is needed.
Checking server version.
Running queries to upgrade MySQL server.
Checking system database.
mysql.columns_priv OK
mysql.db OK
mysql.db_database_info OK
mysql.db_instance_info OK
mysql.db_server_info OK
mysql.engine_cost OK
......................................................
......................................................
Upgrade process completed successfully.
Checking if update is needed.

关于mysql_upgrade的官方先容如下，详细细节参考“4.4.7 mysql_upgrade — Check and Upgrade MySQL Tables”：

mysql_upgrade examines all tables in all databases for incompatibilities with the current version of MySQL Server. mysql_upgrade also upgrades the system tables so that you can take advantage of new privileges or capabilities that might have been added.

If mysql_upgrade finds that a table has a possible incompatibility, it performs a table check and, if problems are found, attempts a table repair. If the table cannot be repaired, see Section 2.11.3, “Rebuilding or Repairing Tables or Indexes” for manual table repair strategies.

You should execute mysql_upgrade each time you upgrade MySQL.

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