查看帮助命令

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MySQL> help; --总的帮助

mysql> help show; --查看show的帮助命令

mysql> help create;--查看create的帮助命令

mysql> help select;--查看select的帮助命令

mysql> help flush;--查看flush的帮助命令

mysql> help reset;--查看reset的帮助命令

查询实例的基本信息

status

查看数据库db1的创建脚本

mysql> show create database db1;

查看表table1的创建脚本

mysql> show create table table1\G 

查询table1表哪些字段有索引，Key有值代表该字段有索引

desc table1

查询table1表的索引，还能看到cardinality信息

show index from table1

查看select语句的执行计划

explain extended select * from t1;

desc extended select * from t1;

查看某个参数

show global variables like '%XX%';

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

查看数据库是否只读

show variables like 'read_only';

查看某个状态

show status like '%YY%';

查看当前连接的客户端数量

show status like 'Threads_connected';

查看服务器的连接次数

show status like 'Connections';

查看曾经的最大连接数

show status like 'Max_used_connections';

查看mysql线程

show full processlist;

查看有多少个数据库

show databases;

查看当前数据库下有多少张表

show tables;

查看各种引擎信息,Support列为DEFAULT表示为当前实例的默认存储引擎

show engines;

查看当前实例的存储引擎设置

show variables like '%engi%'

查看LSN(Log sequence number当前redo log的最新号)

show engine innodb status;

查看当前数据库

select database();

查看当前数据库服务器版本

select version();

查看当前用户

select user();

查询未提交会话的具体SQL

show engine innodb status;查看lock struct信息，比如下面查看到线程是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

查询锁源线程

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)

查询被锁线程

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)

查询XX线程被谁堵塞了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，建议使用sys.schema_table_lock_waits和sys.innodb_lock_waits来查堵塞，不过需要开启参数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

查询user1用户的权限

show grants for user1

查看所有binary日志

show binary logs;

show master logs;

查看当前binary日志文件状态

show master status;

刷新binary日志

flush binary logs;

删除某个binary日志之前的所有日志

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

删除所有的binary log

mysql> reset master;

查询有多少条慢查询记录

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

执行一个10秒的查询

mysql> select sleep(10);

查找持续时间超过 60s 的事务

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

查询所有数据库的数据和索引的大小

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

查询每个数据库的引擎、容量、总表数

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

查询耗CPU的SQL

mysql> show full processlist;

找到Time最大的，其对应的ID列就是耗cpu最厉害的线程ID，对应的Info列就是具体的SQL

或

查看慢查询日志，找到Query_time值最大的行，会记录其线程ID号和具体的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;(此方法需要在从服务启动时指定--report-host=HOSTNAME选项，此处HOSTNAME为任意名称。)

杀线程的SQL，以下两者必须同时使用，其中kill thread_id=kill connection thread_id

mysql>kill query thread_id

mysql>kill thread_id

所有数据库事件的查看

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

单个数据库的事件查看

show events from dbname\G;

禁用某个数据库的某个事件

alter event dbname.eventname disable;

重新收集表的统计信息

analyze table tablename

重建表

alter table tablename engine=innodb

修改表的存储引擎为innodb

alter table tablename engine=innodb

优化表

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

修改proc存储过程的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@%'

本文标题：mysqldba常用的查询语句
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