mysql dba常用的查詢語句

查看幫助命令

mysql> help; --總的幫助

mysql> help show; --查看show的幫助命令

mysql> help create;--查看create的幫助命令

mysql> help select;--查看select的幫助命令

mysql> help flush;--查看flush的幫助命令

mysql> help reset;--查看reset的幫助命令

查詢實例的基本信息

status

查看數據庫db1的創建腳本

mysql> show create database db1;

查看表table1的創建腳本

mysql> show create table table1\G 

查詢table1表哪些字段有索引，Key有值代表該字段有索引

desc table1

查詢table1表的索引，還能看到cardinality信息

show index from table1

查看select語句的執行計劃

explain extended select * from t1;

desc extended select * from t1;

查看某個參數

show global variables like '%XX%';

show global variables where variable_name in ('XX');

查看數據庫是否只讀

show variables like 'read_only';

查看某個狀態

show status like '%YY%';

查看當前連接的客戶端數量

show status like 'Threads_connected';

查看服務器的連接次數

show status like 'Connections';

查看曾經的最大連接數

show status like 'Max_used_connections';

查看mysql線程

show full processlist;

查看有多少個數據庫

show databases;

查看當前數據庫下有多少張表

show tables;

查看各種引擎信息,Support列為DEFAULT表示為當前實例的默認存儲引擎

show engines;

查看當前實例的存儲引擎設置

show variables like '%engi%'

查看LSN(Log sequence number當前redo log的最新號)

show engine innodb status;

查看當前數據庫

select database();

查看當前數據庫服務器版本

select version();

查看當前用戶

select user();

查詢未提交會話的具體SQL

show engine innodb status;查看lock struct信息，比如下面查看到線程是8

1 lock struct(s), heap size 1136, 0 row lock(s), undo log entries 1

MySQL thread id 8, OS thread handle 1358473536, query id 1271 localhost root cleaning up

select sql_text from performance_schema.events_statements_current where THREAD_ID in (select THREAD_ID from performance_schema.threads where PROCESSLIST_ID=8)

或

select b.conn_id,b.thd_id,a.last_statement from sys.session a,sys.processlist b where a.thd_id=b.thd_id and a.conn_id=b.conn_id and b.conn_id=8

查詢鎖源線程

select a.trx_mysql_thread_id,a.* from information_schema.INNODB_TRX a where trx_id in (select blocking_trx_id from information_schema.INNODB_LOCK_WAITS)

查詢被鎖線程

select a.trx_mysql_thread_id,a.* from information_schema.INNODB_TRX a where trx_id in (select requesting_trx_id from information_schema.INNODB_LOCK_WAITS)

查詢XX線程被誰堵塞了select trx_mysql_thread_id blocking_thread,trx_started,trx_query from information_schema.INNODB_TRX where trx_id in

(select blocking_trx_id from information_schema.INNODB_LOCK_WAITS where requesting_trx_id in

(select trx_id from information_schema.INNODB_TRX where trx_mysql_thread_id='XX')

)

5.7.9版本后，建議使用sys.schema_table_lock_waits和sys.innodb_lock_waits來查堵塞，不過需要開啟參數performance_schema=ON

sys.schema_table_lock_waits

select * from sys.schema_table_lock_waits where object_name=`'test'.'t'`\G

select blocking_pid from sys.schema_table_lock_waits where object_name=`'test'.'t'`\G

https://dev.mysql.com/doc/refman/5.7/en/sys-schema-table-lock-waits.html

sys.innodb_lock_waits

select * from sys.innodb_lock_waits where locked_table=`'test'.'t'`\G

select blocking_pid from sys.innodb_lock_waits where locked_table=`'test'.'t'`\G

https://dev.mysql.com/doc/refman/5.7/en/sys-innodb-lock-waits.html

查詢user1用戶的權限

show grants for user1

查看所有binary日志

show binary logs;

show master logs;

查看當前binary日志文件狀態

show master status;

刷新binary日志

flush binary logs;

刪除某個binary日志之前的所有日志

purge binary logs to 'mysql-bin.000003';

刪除所有的binary log

mysql> reset master;

查詢有多少條慢查詢記錄

mysql> show global status like '%Slow_queries%';

執行一個10秒的查詢

mysql> select sleep(10);

查找持續時間超過 60s 的事務

select * from information_schema.innodb_trx where TIME_TO_SEC(timediff(now(),trx_started))>60

查詢所有數據庫的數據和索引的大小

select round(sum(data_length+index_length)/1024/1024) as total_mb,round(sum(data_length)/1024/1024) as data_mb,round(sum(index_length)/1024/1024) as index_mb from information_schema.tables

查詢每個數據庫的引擎、容量、總表數

select table_schema,engine,

round(sum(data_length+index_length)/1024/1024) as total_mb,

round(sum(data_length)/1024/1024) as data_mb,

round(sum(index_length)/1024/1024) as index_mb

count(*) as tables

from information_schema.tables

where table_schema not in('INFORMATION_SCHEMA','PERFORMANCE_SCHEMA') group by table_schema,engine order by 3 desc

查詢耗CPU的SQL

mysql> show full processlist;

找到Time最大的，其對應的ID列就是耗cpu最厲害的線程ID，對應的Info列就是具體的SQL

或

查看慢查詢日志，找到Query_time值最大的行，會記錄其線程ID號和具體的SQL

在master上查看有哪些slave

mysql> select * from information_schema.processlist as p where p.command = 'Binlog Dump';

或

mysql> show slave hosts;(此方法需要在從服務啟動時指定--report-host=HOSTNAME選項，此處HOSTNAME為任意名稱。)

殺線程的SQL，以下兩者必須同時使用，其中kill thread_id=kill connection thread_id

mysql>kill query thread_id

mysql>kill thread_id

所有數據庫事件的查看

select db,name,last_executed,status from mysql.event;

單個數據庫的事件查看

show events from dbname\G;

禁用某個數據庫的某個事件

alter event dbname.eventname disable;

重新收集表的統計信息

analyze table tablename

重建表

alter table tablename engine=innodb

修改表的存儲引擎為innodb

alter table tablename engine=innodb

優化表

optimize table tablename=analyze table tablename + alter table tablename engine=innodb

修改proc存儲過程的definer，比如把'dev_user@%'改成'prod_user@%'
select db,name,type,definer from mysql.proc\G;
update mysql.proc set definer='prod_user@%' where definer='dev_user@%'

修改event事件的definer，比如把'dev_user@%'改成'prod_user@%'
select db,name,definer from mysql.event\G;
update mysql.event set definer='prod_user@%' where definer='dev_user@%'