MYSQL, and Maria DB important commands

Create User
CREATE USER 'ddl'@'%' IDENTIFIED BY 'P@ssw0rd';
GRANT ALL ON ddl.* TO 'ddl'@'%';
FLUSH PRIVILEGES;

List Current DB Users
select User,Host from mysql.user;

To review security and change root password
sudo mysql_secure_installation


To update root password only
UPDATE mysql.user SET Password=PASSWORD('P@ssw0rd') WHERE User='root';
flush privileges;

To get information about DB
select version();
show databases;
use DB_Name
show tables;

Restart database server
sudo service mysql restart

Export/Import DB Backup
mysqldump -u root -p koha_library > kohaBackup.sql

Export:

mysqldump -u username –-password=your_password database_name > file.sql

Import:

mysql -u username –-password=your_password database_name < file.sql 

Compress backup file
tar -czvf kohaBackup.tar.gz kohaBackup.sql


If DB service not start and you need to view the error log
sudo journalctl -xe
tail -30 /var/log/mysql/error.log


Stop/Start/Restart DB service 
sudo service mysqld stop
sudo service mysql stop

sudo service mysql restart

sudo service mysql start
or
sudo service mariadb start

Get current service status
sudo systemctl status mysql.service
or
sudo service mariadb status


Start DB in safe mode
sudo /usr/bin/mysqld_safe


Stop/Start DB in case of error :
systemctl stop mysql.service; systemctl stop mysql.socket
killall mysqld
rm -f /var/run/mysqld/mysqld.sock
systemctl start mysql

Check if MySQL service running 
ps aux | grep mysqld