mysql -u root -p

sudo apt-get install mysql-client-core-5.6

mysql -u root -p

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

sudo apt-get install mysql-server

Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 mysql-server : Depends: mysql-server-5.5 but it is not going to be installed
 E: Unable to correct problems, you have held broken packages.

sudo aptitude install mysql-server

/etc/init.d/mysql start