不知道是不是每次更新 MySQL 軟件之后都需要執行數據庫升級指令？在我進行過的幾次軟件升級之后，總會在 MySQL 的日志中見到
“[ERROR] Missing system table mysql.proxies_priv; please run mysql_upgrade to create it”之類的錯誤。雖然這個錯誤修復起來很簡單，卻不容易引起注意。
1. 錯誤描述
我在好幾次見到這樣的錯誤提示之后才決定好好看看到底寫了些什么。因為網站運行很正常，就心想應該不怎么重要吧。錯誤提示大致內容如下（已將前導的日期時間略去）：
[ERROR] Missing system table mysql.proxies_priv; please run mysql_upgrade to create it
[ERROR] Native table 'performance_schema'.'events_waits_current' has the wrong structure
[ERROR] Native table 'performance_schema'.'events_waits_history' has the wrong structure
[ERROR] Native table 'performance_schema'.'events_waits_history_long' has the wrong structure
[ERROR] Native table 'performance_schema'.'setup_consumers' has the wrong structure
[ERROR] Native table 'performance_schema'.'setup_instruments' has the wrong structure
[ERROR] Native table 'performance_schema'.'setup_timers' has the wrong structure
[ERROR] Native table 'performance_schema'.'performance_timers' has the wrong structure
[ERROR] Native table 'performance_schema'.'threads' has the wrong structure
[ERROR] Native table 'performance_schema'.'events_waits_summary_by_thread_by_event_name' has the wrong structure
[ERROR] Native table 'performance_schema'.'events_waits_summary_by_instance' has the wrong structure
[ERROR] Native table 'performance_schema'.'events_waits_summary_global_by_event_name' has the wrong structure
[ERROR] Native table 'performance_schema'.'file_summary_by_event_name' has the wrong structure
[ERROR] Native table 'performance_schema'.'file_summary_by_instance' has the wrong structure
[ERROR] Native table 'performance_schema'.'mutex_instances' has the wrong structure
[ERROR] Native table 'performance_schema'.'rwlock_instances' has the wrong structure
[ERROR] Native table 'performance_schema'.'cond_instances' has the wrong structure
[ERROR] Native table 'performance_schema'.'file_instances' has the wrong structure
[Note] Event Scheduler: Loaded 0 events
[Note] /usr/libexec/mysqld: ready for connections.
Version: '5.5.20-log' socket: '/var/lib/mysql/mysql.sock' port: 0
有時候可能還會多點兒如下內容：
[ERROR] Incorrect definition of table mysql.proc: expected column 'comment' at position 15 to have type text, found type char(64).
一般看到結尾提示個 ready for connections 一般也就沒心思去看前面都提示了什么東西了。我也是有一次在 x86_64 位 CentOS 中的 MySQL 日志中見到了多出來的這個 ERROR 信息才決定好好看看的前面的錯誤提示的。（我是運行在 32 位 CentOS 上的。）
可是見到錯誤提示句子結構都差不多就沒有仔細往前翻，所以我開始還重新安裝了一遍 MySQL 軟件包。后來才看到每次執行
service mysql restart
重起 MySQL服務的時候都會出現這樣的錯誤提示。然后該錯誤提示開頭還說了，讓執行
mysql_upgrade
指令來修復。才恍然大悟，估計是升級了 MySQL 的軟件包，管理數據庫的某些表結構發生了變化，所以還需要升級數據庫的相關表結構。
2. 修復
mysql_upgrade -u root -p
然后根據提示輸入 mysql 的 root 帳戶密碼，修復過程就可自動運行。此時會有如下形式的提示信息輸出：
mysql_upgrade -u root -p
Enter password:
Looking for 'mysql' as: mysql
Looking for 'mysqlcheck' as: mysqlcheck
Running 'mysqlcheck' with connection arguments: '--port=3306' '--socket=/var/lib/mysql/mysql.sock'
Running 'mysqlcheck' with connection arguments: '--port=3306' '--socket=/var/lib/mysql/mysql.sock'
wp_commentmeta OK
wp_comments OK
wp_links OK
wp_options OK
wp_postmeta OK
wp_posts OK
wp_term_relationships OK
wp_term_taxonomy OK
wp_terms OK
wp_usermeta OK
wp_users OK
mysql.columns_priv OK
mysql.db OK
mysql.event OK
mysql.func OK
mysql.general_log OK
mysql.help_category OK
mysql.help_keyword OK
mysql.help_relation OK
mysql.help_topic OK
mysql.host OK
mysql.ndb_binlog_index OK
mysql.plugin OK
mysql.proc OK
mysql.procs_priv OK
mysql.servers OK
mysql.slow_log OK
mysql.tables_priv OK
mysql.time_zone OK
mysql.time_zone_leap_second OK
mysql.time_zone_name OK
mysql.time_zone_transition OK
mysql.time_zone_transition_type OK
mysql.user OK
Running 'mysql_fix_privilege_tables'... OK
看來每次在 Linux 中升級了 MySQL 軟件包之后都需要進行類似的數據庫升級操作。