Mysql

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Introduction

In the structure of MySQL, there are databases, tables, records, and fields. Databases hold together tables, tables hold together records, records hold together fields, which contain the actual information.

select whithout column names

mysql --skip-column-names

Create user and grant accsess.

GRANT [privileges] ON database.* TO '[user]'@'[host]' IDENTIFIED BY '[password]';
grant all privileges on puppetdb.* to puppet@'localhost' identified by 'puppet';FLUSH PRIVILEGES;

Change root password

mysqladmin -u root password 'new-password'

flush dns

FLUSH HOSTS

Change password

Alternative1.

use mysql;SET PASSWORD FOR 'user'@'hostname' = PASSWORD('passwordhere');

Alternative2.

update mysql.user set password = password() where user = 'username';

Alternative3.

UPDATE mysql.user SET Password=PASSWORD('new-password-here') WHERE User='user-name-here' AND Host='host-name-here';
  • Change password for cacti admin to admin
mysql> update user_auth set password=md5('admin') where username='admin';

backup databases

backup all databases

mysqldump --all-databases -p > /temp/mysql

backup certain databases.

mysqldump --opt -uroot -p --databases IPmon IPdiscover IPcollector > all.sql

backup structure of dabases.

mysqldump --compact --no-data --all-databases > /tmp/database_structure.txt

dump database in innodb consistent way.

mysqldump --single-transaction -u --all-databases > /temp/alldb_june23.sql

Create database

create database puppetdb;

Delete mysql database

drop database puppetdb;

Delete mysql database table

drop table if exists recipes;

Delete row

delete FROM user WHERE id IN (2);

Create table. This creates table with two colums, id with datatype int, and data of the type varchar.

create table testtable (id int, data varchar(100));
CREATE TABLE developers ( name VARCHAR(128), email VARCHAR(128), job VARCHAR(128));
  • Connect to mysql database.
mysql -u root -p password -h mysqlhost

Show databases.

show databases;

Choose database to work with.

use puppetdb;

Show tables

show tables;

Show columns in table.

show columns from hosts;

Show which data is stored in a table in descending order limit to 100

select * from hosts order by id desc limit 100;

Show all data from table

mysql> select * from hosts;

Show all ip in sort ascending order

mysql> select * from hosts order by ip asc;

Show column where page_counter is max in table page. Other values are min, avg, sum

select max(page_counter) from page;

How many rows are on the table.

select count(page_counter) from page;
select count(*) from page;

show value from query

select * from wp_options where option_name='home';

change value in database

UPDATE wp_options SET option_value='http://www.ongamenetwork.com' WHERE option_name='home';

Run sql code. Offen used to setup database.

source /file

Run command in system.

system command

Shows status of database server

status;

Show information about table

describe table;

Show more information about table

show create table table

Put some data into a table

INSERT INTO testtable (id,data) VALUES ('66','The beast whas here');

Change id value 17 to 18 in testtable

UPDATE testtable set id=18 where id=17 ;

Show master/slave status.

show master status \G

Show master/slave status.

show slave status \G

start slave

START SLAVE;

stop slave

stop slave;

Show permission on database

select * from information_schema.user_privileges;

Who has access from which machine.

use mysql;SELECT host,user FROM user;

Import sql script to database.

mysql ongamenetwork < /tmp/ongamenetwork.new.sql

Delete logs

# List logs.
show master logs;
# Delete oldest logs.
purge master logs to 'logfil';

maxconnections in runtime.

show variables like '%connect%';

What is happening in database. Who is connected to database

show processlist;
SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST;
mysql -e 'SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST where NOT COMMAND="Sleep";'

database usage. Is database using myisam or innodb

show table status;

show date

select CURRENT_TIMESTAMP;

show timezone

show variables like '%time%'

mysql server version

select version ();

Reset mysql root password

Stop the MySql server.
/usr/bin/mysqld_safe --skip-grant-tables &
mysql -h localhost
use mysql
update user set password = password('.......') where user = 'root' and host='localhost';
quit
Restart the server and run as normal.

Data types

Numerical, signed=could be negative,unsigned

type		Maxvalue
tinyint		255
smallint	65535
mediumint	16777215
int		4294967295
bigint		18446744073709551615

Strings

type			Maxvalue
varchar			255
char			255
tinyblob,tinytext	256
blob,text		65536
mediumblob,mediumtext	16777216
longblob,longtext	4294967296

Special

date
timestamp

Access types.

ALL 		- Gives the all privilege control for the database
CREATE		- Allows users to create tables
SELECT		- Allows users to query tables
INSERT		- Allows users to insert data into a table
SHOW DATABASES	- Allows users to see a list of databases
USAGE		- User has no privileges
GRANT OPTION	- Allows users to grant privileges

auto submit password

.my.cnf 

[client]
user=user_name
pass=password

replication master slave

Setting the Replication Master Configuration

/etc/my.cnf 

[mysqld]
log-bin=mysql-bin
server-id=1

To get the master status information, follow these steps:
Start the command line client and flush all tables and block write statements by executing the FLUSH TABLES WITH READ LOCK statement:
mysql> FLUSH TABLES WITH READ LOCK;
Leave the client from which you issued the FLUSH TABLES statement running so that the read lock remains in effect. If you exit the client, the lock is released.

mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 |       98 |              |                  |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

The File column shows the name of the log and Position shows the offset within the file. In this example, the binary log file is mysql-bin.000001 and the offset is 98. Record these values. You need them later when you are setting up the slave. They represent the replication coordinates at which the slave should begin processing new updates from the master.

If the master has been running previously without binary logging enabled, the log name and position values displayed by SHOW MASTER STATUS or mysqldump --master-data will be empty. In that case, the values that you need to use later when specifying the slave's log file and position are the empty string () and 4.

mysqldump --all-databases --lock-all-tables >/tmp/dbdump.db

mysql> GRANT REPLICATION SLAVE ON *.* TO 'replication'@'192.168.7.%' IDENTIFIED BY 'slavepass';

Setting the Replication Slave Configuration

/etc/my.cnf 

[mysqld]
server-id=2

Import the dump file: 

shell> mysql < /tmp/dbdump.db

mysql> CHANGE MASTER TO MASTER_HOST='192.168.7.30', MASTER_USER='replication', MASTER_PASSWORD='slavepass', MASTER_LOG_FILE='mysql-bin.000001',MASTER_LOG_POS=98, MASTER_PORT='3307';

Start the slave threads: 

mysql> START SLAVE;

Once a slave is replicating, you can find in its data directory one file named master.info and another named relay-log.info.

Test to verify functionality of slave database

the existence of these three lines verifies that the slave is functioning well. 

mysql -e 'show slave status\G' |grep -E 'Slave_IO_Running:|Slave_SQL_Running:|Seconds_Behind_Master:'
            Slave_IO_Running: Yes
           Slave_SQL_Running: Yes
       Seconds_Behind_Master: 0

Usage of database files/size

This query will output Data_length and Index_length for each table in your database. If you add them all together you can get the size used for your particular database. 

show table status;

Usage of database. 

SELECT table_schema "Data Base Name", sum( data_length + index_length ) / 1024 / 1024 "Data Base Size in MB" FROM information_schema.TABLES GROUP BY table_schema ;

Show size of every table in database 

SELECT 
     table_schema as `Database`, 
     table_name AS `Table`, 
     round(((data_length + index_length) / 1024 / 1024), 2) `Size in MB` 
FROM information_schema.TABLES 
ORDER BY (data_length + index_length) DESC;

pager

Put output to file instead standard output. 

\P cat > /tmp/tmp

fix database/check database

All databases. 

mysqlcheck -c -u root -ppassword --all-databases

Check one database 

mysqlcheck -c database -u root -ppassword

look at health of slave database

select @@hostname,now();show variables like 'read_only';show slave status\G

mysqld man page

/usr/libexec/mysqld  --verbose --help

last row

SELECT fields FROM table ORDER BY id DESC LIMIT 1;

enable disable full log

# WARNING. generates lot of data and slow down database. Enable general_log_file. Logs each queury against database.
mysql -e "SET global log_output = 'FILE'; SET global general_log_file='queries.log'; SET global general_log = 1;"

# can be turned off with
mysql -e "SET global general_log = 0;"

# Look at queries
tail -f /apps/mysql/data/queries.log

# Clean log.
:>/apps/mysql/data/queries.log

# If you dont find logfile do. Has to be enabled at the time.
lsof | grep /queries.log

show constrains on tables

SHOW CREATE TABLE table;

kill query

KILL QUERY "ID";

Fragmentation

data_free are the holes in the database. 

mysql -e 'select ENGINE, TABLE_NAME,Round( DATA_LENGTH/1024/1024) as data_length , round(INDEX_LENGTH/1024/1024) as index_length, round(DATA_FREE/ 1024/1024) as data_free from information_schema.tables  where  DATA_FREE > 0;'

truncate table

Truncate table 

TRUNCATE TABLE table_name

explain

EXPLAIN SELECT * FROM categories\G

innodb tables list

list innodb tables 

SELECT table_schema, table_name FROM INFORMATION_SCHEMA.TABLES WHERE engine = 'innodb';

alter table

Read fragmented innodb file from disk, Lock table, Store table back on disk without holes 

ALTER TABLE table ENGINE=INNODB;

optimize execution

SET SESSION optimizer_search_depth = 5;

mysql_upgrade

After updating mysql run the following command to update tables. 

mysql_upgrade

unlock tables

UNLOCK TABLES;
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