How to query quickly in mysql

Mysql quick query method: 1. Query the running transaction; 2. Check the current connection and know the number of connections; 3. Check the size of a table; 4. Check the size of all tables in a database size.

More related free learning recommendations: mysql tutorial(video)

mysql quick query method:

1. Query the running transaction

select p.id,p.user,p.host,p.db,p.command,p.time,i.trx_state,i.trx_started,p.info  from information_schema.processlist p,information_schema.innodb_trx i where p.id=i.trx_mysql_thread_id;

2. View the current connection and know the number of connections

select SUBSTRING_INDEX(host,‘:‘,1) as ip , count(*) from information_schema.processlist group by ip;

3 .Check the size of a table

select concat(round(sum(DATA_LENGTH/1024/1024),2),‘M‘) from information_schema.tables where table_schema=‘数据库名‘ AND table_name=‘表名‘;

4.Check the size of all tables in a database

select table_name,concat(round(sum(DATA_LENGTH/1024/1024),2),‘M‘)  from information_schema.tables where table_schema=‘t1‘ group by table_name;

5.Check the size of the library and the remaining space

select table_schema,round((sum(data_length / 1024 / 1024) + sum(index_length / 1024 / 1024)),2) dbsize,round(sum(DATA_FREE / 1024 / 1024),2) freesize,       
round((sum(data_length / 1024 / 1024) + sum(index_length / 1024 / 1024)+sum(DATA_FREE / 1024 / 1024)),2) spsize  
from information_schema.tables 
where table_schema not in (‘mysql‘,‘information_schema‘,‘performance_schema‘) 
group by table_schema order by freesize desc;

6. Find out about the use of lock

select r.trx_id waiting_trx_id,r.trx_mysql_thread_id waiting_thread,r.trx_query waiting_query,b.trx_id blocking_trx_id,b.trx_mysql_thread_id blocking_thread,b.trx_query blocking_query  
from information_schema.innodb_lock_waits w 
inner join information_schema.innodb_trx b 
on b.trx_id = w.blocking_trx_id 
inner join information_schema.innodb_trx r on r.trx_id = w.requesting_trx_id\G

information_schema

1. Check the table data size under each library

select table_name,concat(round(sum(DATA_LENGTH/1024/1024),2),‘M‘) 
from information_schema.tables where table_schema=‘db_name‘ group by table_name;

2. Check the data size of each database

select TABLE_SCHEMA, concat(round(sum(data_length)/1024/1024,2),‘ MB‘) as data_size  from information_schema.tables group by table_schema;

3. Check whether the instance has a primary key

select table_schema,table_name from information_schema.tables 
where (table_schema,table_name) 
not in(select distinct table_schema,table_name from information_schema.STATISTICS where INDEX_NAME=‘PRIMARY‘ ) 
and table_schema not in ( ‘sys‘,‘mysql‘,‘information_schema‘,‘performance_schema‘);

4. Check which fields in the instance can be null

select TABLE_SCHEMA,TABLE_NAME from COLUMNS where IS_NULLABLE=‘YES‘ and TABLE_SCHEMA not in (‘information_schema‘,‘performance_schema‘,‘mysql‘, ‘sys‘)\G

5. Check what stored procedures and functions are in the instance

#存储过程
select ROUTINE_SCHEMA,ROUTINE_NAME,ROUTINE_TYPE
from information_schema.ROUTINES
where ROUTINE_TYPE=‘PROCEDURE‘ and ROUTINE_SCHEMA not in (‘mysql‘,‘sys‘,‘information_schema‘,‘performance_schema‘);
#函数
select ROUTINE_SCHEMA,ROUTINE_NAME,ROUTINE_TYPE 
from information_schema.ROUTINES 
where ROUTINE_TYPE=‘FUNCTION‘ and ROUTINE_SCHEMA not in (‘mysql‘,‘sys‘,‘information_schema‘,‘performance_schema‘);

6. Check which table field character sets in the instance are inconsistent with the default character set

select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,CHARACTER_SET_NAME 
from information_schema.COLUMNS 
where (CHARACTER_SET_NAME is null or CHARACTER_SET_NAME <> ‘utf8‘) 
and TABLE_SCHEMA not in (‘information_schema‘,‘performance_schema‘,‘test‘,‘mysql‘,‘sys‘);

7. Check which table field character verification rules in the instance are inconsistent with the default

Check the current character set and collation rule settings

show variables like ‘collation_%‘;
select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,CHARACTER_SET_NAME,COLLATION_NAME 
from information_schema.COLUMNS 
where (COLLATION_NAME is null or COLLATION_NAME <> ‘utf8_general_ci‘) 
and TABLE_SCHEMA not in (‘information_schema‘,‘performance_schema‘,‘test‘,‘mysql‘,‘sys‘);

8. Check which accounts have permissions other than select, update, and insert

select GRANTEE,PRIVILEGE_TYPE,concat(TABLE_SCHEMA,‘-‘,TABLE_NAME,‘-‘,COLUMN_NAME) from COLUMN_PRIVILEGES where PRIVILEGE_TYPE not in (‘select‘,‘insert‘,‘update‘)
union 
select GRANTEE,PRIVILEGE_TYPE,TABLE_SCHEMA from SCHEMA_PRIVILEGES where PRIVILEGE_TYPE not in (‘select‘,‘insert‘,‘update‘)
union
select GRANTEE,PRIVILEGE_TYPE,concat(TABLE_SCHEMA,‘-‘,TABLE_NAME) from TABLE_PRIVILEGES where PRIVILEGE_TYPE not in (‘select‘,‘insert‘,‘update‘) 
union
select GRANTEE,PRIVILEGE_TYPE,concat(‘user‘) from USER_PRIVILEGES where PRIVILEGE_TYPE not in (‘select‘,‘insert‘,‘update‘);

9. Check which tables in the instance are not the default storage engine to The default storage engine is innodb as an example

select TABLE_NAME,ENGINE 
from information_schema.tables 
where ENGINE!=‘innodb‘ and TABLE_SCHEMA not in (‘information_schema‘,‘performance_schema‘,‘test‘,‘mysql‘, ‘sys‘);

10. Check which tables in the instance have foreign keys

select a.TABLE_SCHEMA,a.TABLE_NAME,a.CONSTRAINT_TYPE,a.CONSTRAINT_NAME,b.REFERENCED_TABLE_NAME,b.REFERENCED_COLUMN_NAME 
from information_schema.TABLE_CONSTRAINTS a LEFT JOIN information_schema.KEY_COLUMN_USAGE b 
ON a.CONSTRAINT_NAME=b.CONSTRAINT_NAME where a.CONSTRAINT_TYPE=‘FOREIGN KEY‘;

11. Check which table fields in the instance have cascading updates

select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,REFERENCED_TABLE_SCHEMA,REFERENCED_TABLE_NAME,REFERENCED_COLUMN_NAME 
from information_schema.KEY_COLUMN_USAGE 
where REFERENCED_TABLE_SCHEMA is not null 
and REFERENCED_TABLE_NAME is not null 
and REFERENCED_COLUMN_NAME is not null and table_schema not in (‘information_schema‘,‘performance_schema‘,‘test‘,‘mysql‘, ‘sys‘);

12. How to filter the connection information in the current instance based on user name, connection time, executed sql, etc.

select USER,HOST,DB from processlist where TIME>2;

13. View tables without indexes in the database

select TABLE_SCHEMA,TABLE_NAME from information_schema.tables 
where TABLE_NAME  not in (select distinct(any_value(TABLE_NAME))  from information_schema.STATISTICS group by INDEX_NAME) 
and TABLE_SCHEMA not in (‘sys‘,‘mysql‘,‘information_schema‘,‘performance_schema‘);

14. View the tables in the database Indexed tables, which indexes have been established

Display results: library name, table name, index name

select TABLE_SCHEMA,TABLE_NAME,group_concat(INDEX_NAME) 
from  information_schema.STATISTICS where TABLE_SCHEMA not in (‘sys‘,‘mysql‘,‘information_schema‘,‘performance_schema‘)  group by TABLE_NAME ;

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