mysqldba常用的查询语句
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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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