apt-get remove --purge mysql*

apt-get install mysql-server-5.6 mysql-client-5.6

service mysql restart
or
service mysql start
or
systemctl restart mysql
or
systemctl start mysql

Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.

systemctl status mysql

mysql.service - LSB: Start and stop the mysql database server daemon
   Loaded: loaded (/etc/init.d/mysql; bad; vendor preset: enabled)
   Active: failed (Result: exit-code) since Mon 2017-04-10 13:24:00 EDT; 29s ago
     Docs: man:systemd-sysv-generator(8)
  Process: 15820 ExecStart=/etc/init.d/mysql start (code=exited, status=1/FAILURE)
 Main PID: 1323 (code=exited, status=0/SUCCESS)

Apr 10 13:23:30 server mysqld[15926]: 2017-04-10 13:23:30 15925 [Note] InnoDB: Compressed tables use zlib 1.2.8
Apr 10 13:23:30 server mysqld[15926]: 2017-04-10 13:23:30 15925 [Note] InnoDB: Using Linux native AIO
Apr 10 13:23:30 server mysqld[15926]: 2017-04-10 13:23:30 15925 [Note] InnoDB: Using CPU crc32 instructions
Apr 10 13:23:30 server mysqld[15926]: 2017-04-10 13:23:30 15925 [Note] InnoDB: Initializing buffer pool, size = 128.0M
Apr 10 13:23:30 server mysqld[15926]: 2017-04-10 13:23:30 15925 [Note] InnoDB: Completed initialization of buffer pool
Apr 10 13:24:00 server mysql[15820]:    ...fail!
Apr 10 13:24:00 server systemd[1]: mysql.service: Control process exited, code=exited status=1
Apr 10 13:24:00 server systemd[1]: Failed to start LSB: Start and stop the mysql database server daemon.
Apr 10 13:24:00 server systemd[1]: mysql.service: Unit entered failed state.
Apr 10 13:24:00 server systemd[1]: mysql.service: Failed with result 'exit-code'.

Apr 10 13:23:30 server mysqld: 2017-04-10 13:23:30 15925 [Note] InnoDB: Completed initialization of buffer pool
Apr 10 13:23:30 server mysqld_safe: mysqld from pid file /var/lib/mysql/server.pid ended
Apr 10 13:24:00 server /etc/init.d/mysql[16277]: 0 processes alive and '/usr/bin/mysqladmin --defaults-file=/etc/mysql/debian.cnf ping' resulted in
Apr 10 13:24:00 server /etc/init.d/mysql[16277]: #007/usr/bin/mysqladmin: connect to server at 'localhost' failed
Apr 10 13:24:00 server /etc/init.d/mysql[16277]: error: 'Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)'
Apr 10 13:24:00 server /etc/init.d/mysql[16277]: Check that mysqld is running and that the socket: '/var/run/mysqld/mysqld.sock' exists!
Apr 10 13:24:00 server /etc/init.d/mysql[16277]:
Apr 10 13:24:00 server mysql[15820]:    ...fail!
Apr 10 13:24:00 server systemd[1]: mysql.service: Control process exited, code=exited status=1
Apr 10 13:24:00 server systemd[1]: Failed to start LSB: Start and stop the mysql database server daemon.
Apr 10 13:24:00 server systemd[1]: mysql.service: Unit entered failed state.
Apr 10 13:24:00 server systemd[1]: mysql.service: Failed with result 'exit-code'.

170410 13:33:28 mysqld_safe Logging to syslog.
170410 13:33:28 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
170410 13:33:28 mysqld_safe mysqld from pid file /var/lib/mysql/server.pid ended

#
# The MySQL database server configuration file.
#
# You can copy this to one of:
# - "/etc/mysql/my.cnf" to set global options,
# - "~/.my.cnf" to set user-specific options.
#
# One can use all long options that the program supports.
# Run program with --help to get a list of available options and with
# --print-defaults to see which it would actually understand and use.
#
# For explanations see
# http://dev.mysql.com/doc/mysql/en/server-system-variables.html

# This will be passed to all mysql clients
# It has been reported that passwords should be enclosed with ticks/quotes
# escpecially if they contain "#" chars...
# Remember to edit /etc/mysql/debian.cnf when changing the socket location.

# Here is entries for some specific programs
# The following values assume you have at least 32M ram

!includedir /etc/mysql/conf.d/

sudo service mysql stop

sudo apt-get remove mysql
sudo apt-get purge mysql